Process for electrocoating metal blanks and coiled metal substrates

ABSTRACT

Processes for forming a coating on electroconductive flat blanks having two major surfaces and sheared edges are provided. Also provided is a process for forming a multi-composite coating on a pre-sheared, electroconductive, flat blank having two major surfaces and sheared edges. Methods for forming and coating metal blanks are also provided. The present invention further provides a pre-sheared, flat electroconductive blank having two major surfaces and coated with a multi-layer composite coating composition on one major surface. The present invention also provides a method for coating a continuous metal strip, optionally, thereafter forming a coated blank therefrom, and, optionally, applying a second coating to the blank.

This application is a divisional application of U.S. patent applicationSer. No. 10/459,968, filed Jun. 12, 2003, now U.S. Pat. No. 7,285,200,which is divisional application of U.S. patent application Ser. No.09/798,627, filed Mar. 2, 2001, now U.S. Pat. No. 6,676,820, which isincorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to processes for electrocoatingpre-sheared metal blanks as well as to processes for electrocoatingcoiled metal substrates and subsequently forming metal blanks from theelectrocoated substrates.

BACKGROUND OF THE INVENTION

Electrodeposition as a coating application method involves deposition ofa film-forming composition onto a conductive substrate under theinfluence of an applied electrical potential. Electrodeposition hasbecome increasingly important in the coatings industry because, bycomparison with non-electrophoretic coating means, electrodepositionoffers increased paint utilization, improved corrosion protection andlow environmental contamination.

Initially, electrodeposition was conducted with the workpiece beingcoated serving as the anode. This was familiarly referred to as anionicor anodic electrodeposition. However, in 1972, cationic (or cathodic)electrodeposition was introduced commercially. Since that time, cationicelectrodeposition has steadily gained in popularity and today is by farthe most prevalent method of electrodeposition. For example, throughoutthe world, more than 80 percent of all motor vehicles produced are givena primer coating by cationic electrodeposition.

Multilayered coating composites for metal substrates, for example,substrates used in the appliance and automobile industries, typicallyhave involved electrodeposition coatings as an initial resinous coatinglayer to protect the metal substrate from corrosion. However, two-coatapplication by the electrodeposition process is known in the art. Forexample U.S. Pat. Nos. 4,988,420; 4,840,715; and 5,275,707 disclosemulti-layered composite coatings applied by electrodeposition whereinelectroconductive pigments are included in a first electrodepositedacrylic resinous coating, and subsequently a second coating iselectrodeposited over the conductive first coating. Typically, thesesecond electrodeposition coatings are applied for durability anddecorative purposes.

The term “blank” refers to a flat or substantially flat section cut or“sheared” from a coiled metal strip and subsequently formed into a part,such as front and side panels for appliances, e.g., refrigerators,washers and dryers, metal office furniture, e.g., filing cabinets anddesks, and building products, e.g., fluorescent lighting fixtures. Oftenholes must be punched in the blanks.

Coated metal blanks can offer many advantages in the manufacture of suchproducts. Coated blanks can be “stacked” for storage in a verticalstacker while awaiting subsequent coating, forming, fastening and/orassembly processes. This can result in a reduction of inventory storagespace as well as a reduction in in-process inventory. Also, primed-onlyblanks which have been cut to specification for various end-use productscan be stacked off-line awaiting subsequent top coating steps. A widevariety of top coating compositions (e.g., liquid coatings and powdercoatings) can be applied to the primed blanks using various applicationtechniques, for example, electrodeposition, spray or roll coatingtechniques. In this way, a wide variety of colors can be delivered in arelatively short time.

As mentioned above, blanks can be cut from pre-coated or pre-paintedcoiled metal substrates or, alternatively, from coiled metal stock priorto coating the coiled metal. Problems can arise when blanks are cut frompre-coated metal. The shearing of these blanks (thus creating blankshaving “sheared edges”) and the hole punching process typically createsexposed sheared ends and edges (i.e., edges devoid of protectivecoating), thus necessitating application of additional corrosioninhibitors to these areas. Special corrosion protection is especiallycritical if the finished product is subjected to high humidityconditions or aggressive detergents. Moreover, the coil-applied coatingmust meet strict flexibility requirements in order to withstand theshearing and punching processes without fracturing and/or losingadhesion at the edges of the sheared/punched area, as well aspost-forming processes.

For the above-stated reasons, blanks cut from uncoated coiled metalstock, which are subsequently coated and formed into parts, can offerseveral advantages. First, sheared ends and edges are coated during theoverall coating process, thus eliminating the additional step ofapplying a corrosion inhibitor to these edges. Further, although thecoatings applied to pre-sheared blanks must meet the flexibilityrequirements necessary for withstanding post-forming processes, the needfor coatings capable of withstanding the harsh shearing and punchingprocesses is eliminated.

U.S. Pat. No. 5,439,704 teaches a combined coil and blank powder coatingline which has the capability of coating coiled metal strips to formpre-coated metal coil stock as well as coating pre-sheared and/orpunched blanks with the same coating line. Due to the necessity ofplacing the blanks on a horizontal support surface for transport,however, only the topside of the blank can be powder coated, thusleaving the underside uncoated.

U.S. Pat. No. 5,908,667 discloses a process for producing a multilayerlacquer coating of low dry film thickness in which a primer of anelectrodepositable aqueous coating composition is electrophoreticallyapplied onto (presumably both sides of) a conductive substrate andsubsequently cured to form an electrically conductive primer on thesubstrate. A base coat is formed thereover by electrodeposition of acolor-giving and/or effect-producing aqueous electrodepositable coatingcomposition. The multilayer coating process is particularly useful forcoating automobiles or pre-formed automobile parts.

It would be desirable to provide a post-formable, multi-layer compositecoating on a metal blank using, at least in part, an electrodepositionprocess. The process would advantageously include electrodeposition of acorrosion inhibitive conductive primer to the blank surfaces followed byelectrodeposition of an appearance enhancing top coat, or,alternatively, application of a non-electrophoretic top coating. Such aprocess would provide the aforementioned desired coating properties withefficient paint utilization and fast cure times.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart depicting the shearing and coating steps used inthe processes of the present invention for forming and coating blanksand/or continuous metal strips.

FIG. 2 is a side, schematic view (not to scale) of an exemplaryelectrocoating apparatus incorporating features of the invention;

FIG. 3 is a sectional view of the electrocoating apparatus of FIG. 2taken along the line III-III;

FIG. 4 is an enlarged view of an exemplary connecting system of theelectrocoating apparatus shown in FIG. 2.

SUMMARY OF THE INVENTION

The present invention is directed to a process for forming a coating ona pre-sheared, electroconductive flat blank having two major surfacesand sheared edges. The process comprises the steps of (1) conveying theblank to an electrodeposition bath located on a coating line; (2)applying an aqueous electrodepositable coating composition to both majorsurfaces and the sheared edges of the blank as the blank passes throughthe electrodeposition bath, the blank serving as an electrode in anelectrical circuit comprising the electrode and a counter-electrodeimmersed in the aqueous electrodepositable coating composition, thecomposition being deposited onto both major surfaces and the shearededges of the blank as a substantially continuous coating as electriccurrent is passed between the electrodes; (3) conveying the coated blankof step (2) from the electrodeposition bath to a drying station locatedon the coating line; and (4) drying the electrodeposited coating as itpasses through the drying station.

The present invention is also directed to a process for forming amulti-composite coating on a pre-sheared, electroconductive, flat blankhaving two major surfaces and sheared edges. The process comprises thesteps of (1) conveying the blank to a first electrodeposition bathlocated on a coating line; (2) applying a first aqueouselectrodepositable coating composition to both major surfaces and thesheared edges of the blank as it passes through the electrodeposition,the blank serving as an electrode in an electrical circuit comprisingthe electrode and a counter-electrode immersed in the aqueouselectrodepositable coating composition, the composition being depositedonto both major surfaces and the sheared edges of the blank as asubstantially continuous electroconductive coating as electric currentis passed between the electrodes; (3) optionally, conveying the coatedblank of step (2) from the first electrodeposition bath to a firstdrying station located on the coating line; and drying theelectroconductive coating as it passes through the first drying station;(4) conveying the coated blank of step (2) or, optionally, step (3), toa second electrodeposition bath located on the coating line; (5)applying a second electrodepositable coating composition to the coatedblank as it passes through the second electrodeposition bath, the blankserving as an electrode in an electrical circuit comprising theelectrode and a counter-electrode immersed in the second aqueouselectrodepositable coating composition, the composition being depositedonto one of the major surfaces of the coated blank as a substantiallycontinuous electrically insulating coating as electric current is passedbetween the electrodes; (6) conveying the coated blank of step (5) to adrying station located on the coating line; and (7) drying theelectrically insulating coating as the blank of step (6) passes throughthe drying station.

Also, the present invention is directed to a pre-sheared, flatelectroconductive blank having two major surfaces and coated with amulti-layer composite coating composition on one major surface. Themulti-layer composite coating composition comprises (a) acorrosion-resistant, electrically conductive first coatingelectrodeposited over both major surfaces of the blank from a firstaqueous electrodepositable coating composition. The first aqueouselectrodepositable coating composition comprises (i) anelectrodepositable ionic resin, and (ii) one or more electricallyconductive pigments. An appearance enhancing, electrically insulatingtop coating is electrodeposited over the electrically conductive firstcoating on one major surface of the blank from an aqueouselectrodepositable top coating composition.

The present invention is also further directed to various methods forforming and coating metal blanks. In one embodiment of the presentinvention, the method comprises the steps of (1) supplying a continuousmetal strip from a coil through an entrance of a shear located prior toan entrance end of an electrodeposition bath located on a coating line;(2) shearing the metal strip to form a blank having two major surfacesand sheared edges as the metal strip passes through the shear; (3)conveying the blank formed in step (2) to the electrodeposition bath;(4) applying one of the previously described electrodepositable coatingcomposition to the blank as it passes through the bath, the blankserving as an electrode in an electrical circuit comprising theelectrode and a counter-electrode immersed in the aqueouselectrodepositable coating composition, the composition being depositedonto both major surfaces and the sheared edges of the blank as asubstantially continuous coating as electric current is passed betweenthe electrodes; (5) conveying the coated blank of step (4) to a dryingstation located on the coating line; and (6) drying the coated blank asit passes through the drying station.

In another embodiment, the present invention is directed to a method forforming and coating metal blanks comprising the steps of (1) supplying acontinuous metal strip from a coil through an entrance of a shearlocated prior to an entrance end of a first electrodeposition bathlocated on a coating line; (2) shearing the metal strip to form a blankhaving two major surfaces and sheared edges as the metal strip passesthrough the shear; (3) conveying the blank formed in step (2) to thefirst electrodeposition bath; (4) applying a first aqueouselectrodepositable coating composition to both major surfaces and thesheared edges of the blank as it passes through the firstelectrodeposition bath, the blank serving as an electrode in anelectrical circuit comprising the electrode and a counter-electrodeimmersed in the first aqueous electrodepositable coating composition,the composition being deposited onto both major surfaces and the shearededges of the blank as a substantially continuous electrically conductivecoating as electric current is passed between the electrodes; (5)optionally, conveying the coated blank of step (4) to a first dryingstation located in the coating line, and drying the coated blank as itpasses through the drying station; (6) conveying the coated blank ofstep (4) or, optionally, step (5) to a second electrodeposition bathlocated on the coating line; (7) applying a second electrodepositablecoating composition to the coated blank as it passes through the secondelectrodeposition bath, the blank serving as an electrode in anelectrical circuit comprising the electrode and a counter-electrodeimmersed in the second aqueous electrodepositable coating composition,the composition being deposited onto one of the major surfaces of thecoated blank as a substantially continuous electrically insulatingcoating as electric current is passed between the electrodes; (8)conveying the coated blank of step (7) to a drying station located onthe coating line; and (9) drying the electrically insulating coating asthe blank passes through the drying station.

The present invention is also directed to methods for coating acontinuous metal strip and thereafter forming a coated blank therefrom.In one embodiment, the method comprises the steps of (1) supplying acontinuous metal strip having two major surfaces to the entrance of anelectrodeposition bath located on a coating line; (2) applying anelectrodepositable coating composition to both major surfaces of themetal strip as it passes through the bath, the metal strip serving as anelectrode in an electrical circuit comprising the electrode and acounter-electrode immersed in the aqueous electrodepositable coatingcomposition, the composition being deposited onto both major surfaces ofthe metal strip as a substantially continuous coating as electriccurrent is passed between the electrodes; (3) conveying the metal stripfrom step (2) to a drying station located on the coating line; (4)drying the electrodeposited coating as the metal strip passes throughthe drying station; (5) optionally, conveying the coated metal stripfrom step (4) to a recoiling station and recoiling the coated metalstrip; (6) conveying the coated metal strip from step (4) or,optionally, the recoiled coated metal strip of step (5) to an entranceof a shear located at an exit end of the drying station; and (7)shearing the coated metal strip to form a coated blank as the strippasses through the shear.

Additionally, the present invention is directed to a method for coatinga continuous metal strip, thereafter forming a coated blank therefromand then applying a second coating to the blank. The method comprisesthe steps of (1) supplying a continuous metal strip having two majorsurfaces to an entrance of an electrodeposition bath located on acoating line; (2) applying a first electrodepositable coatingcomposition to both major surfaces of the metal strip as it passesthrough the bath, the metal strip serving as an electrode in anelectrical circuit comprising the electrode and a counter-electrodeimmersed in the first aqueous electrodepositable coating composition,the composition being deposited onto both major surfaces of the metalstrip as a substantially continuous electrically conductive coating aselectric current is passed between the electrodes; (3) optionally,conveying the metal strip from step (2) to a first drying stationlocated on the coating line, and drying the electrically conductivecoating as the metal strip passes through the first drying station; (4)optionally, conveying the coated metal strip of step (3) to a recoilingstation located off the coating line, and recoiling the coated metalstrip; (5) transferring the coated metal strip from step (2), or,optionally, step (3) or step (4) to an entrance of a shear located at anexit end of the drying station; (6) shearing the coated metal strip toform a coated blank as the metal strip passes through the shear; (7)conveying the coated blank from step (6) to a second electrodepositionbath located in the coating line; (8) applying a secondelectrodepositable coating composition to one of the major surfaces ofthe coated blank as it passes through the second electrodeposition bath,the blank serving as an electrode in an electrical circuit comprisingthe electrode and a counter-electrode immersed in the second aqueouselectrodepositable coating composition, the composition being depositedonto one major surface of the coated blank as a substantially continuouselectrically insulating coating as electric current is passed betweenthe electrodes; (9) conveying the coated blank of step (8) to a dryingstation located on the coating line; and (10) drying the electricallyinsulating coating as the blank of step (9) passes through the dryingstation.

The present invention is also directed to a method for coating acontinuous metal strip and thereafter forming a coated blank therefromcomprising the steps of (1) supplying a continuous metal strip havingtwo major surfaces to an entrance of an electrodeposition bath locatedon a coating line; (2) applying a first electrodepositable coatingcomposition to both major surfaces of the metal strip as it passesthrough the bath, the metal strip serving as an electrode in anelectrical circuit comprising the electrode and a counter-electrodeimmersed in the first aqueous electrodepositable coating composition,the composition being deposited onto both major surfaces of the metalstrip as a substantially continuous electrically conductive coating aselectric current is passed between the electrodes; (3) optionally,conveying the metal strip from step (2) to a first drying stationlocated on the coating line, and drying the electrically conductivecoating as the metal strip passes through the first drying station; (4)optionally, conveying the coated metal strip of step (3) to a recoilingstation located off the coating line, and recoiling the coated metalstrip; (5) conveying the coated metal strip from step (3) or, optionallystep (4) to a second electrodeposition bath located on the coating line;(6) applying a second electrodepositable coating composition to one ofthe major surfaces of the coated metal strip as it passes through thesecond electrodeposition bath, the metal strip serving as an electrodein an electrical circuit comprising the electrode and acounter-electrode immersed in the second aqueous electrodepositablecoating composition, the composition being deposited onto one of themajor surfaces of the coated metal strip as a substantially continuouselectrically insulating coating as electric current is passed betweenthe electrodes; (7) conveying the coated metal strip of step (6) to adrying station located on the coating line; (8) drying the electricallyinsulating coating as the coated metal strip of step (7) passes throughthe drying station; (9) optionally, transferring the coated metal stripof step (8) to a recoiling station located off the coating line, andrecoiling the coated metal strip; (10) transferring the coated metalstrip from step (8), or, optionally, step (9) to an entrance of a shearlocated at an exit end of the drying station; and (11) shearing thecoated metal strip to form a coated blank as the metal strip passesthrough the shear.

In a further embodiment, the present invention is directed to a methodfor forming a coating on one major surface of a pre-sheared,electroconductive, flat blank having two major surfaces and shearededges. The method comprises the steps of (1) conveying the blank to anelectrodeposition bath located on a coating line; (2) applying anaqueous electrodepositable coating composition to one major surface andthe sheared edges of the blank as the blank passes through theelectrodeposition bath, the blank serving as an electrode in anelectrical circuit comprising the electrode and a counter-electrodeimmersed in the aqueous electrodepositable coating composition, thecomposition being deposited onto one major surface and the sheared edgesof the blank as a substantially continuous coating as electric currentis passed between the electrodes; (3) conveying the coated blank of step(2) from the electrodeposition bath to a drying station located on thecoating line; and (4) drying the electrodeposited coating as it passesthrough the drying station.

Also, the present invention is directed to a method for forming andcoating metal blanks comprising (1) supplying a continuous metal stripfrom a coil through an entrance of a shear located prior to an entranceend of an electrodeposition bath located on a coating line; (2) shearingthe metal strip to form a flat blank having two major surfaces andsheared edges as the metal strip passes through the shear; (3) conveyingthe blank formed in step (2) to the electrodeposition bath; (4) applyingan electrodepositable coating composition to the blank as it passesthrough the bath, the blank serving as an electrode in an electricalcircuit comprising the electrode and a counter-electrode immersed in theaqueous electrodepositable coating composition, the composition beingdeposited onto one major surface and the sheared edges of the blank as asubstantially continuous coating as electric current is passed betweenthe electrodes; (5) conveying the coated blank of step (4) to a dryingstation located on the coating line; and (6) drying the coated blank asit passes through the drying station.

The present invention also provides a method for coating a continuousmetal strip comprising (1) supplying a continuous metal strip having twomajor surfaces to the entrance of an electrodeposition bath located on acoating line; (2) applying an electrodepositable coating composition toone major surface of the metal strip as it passes through the bath, themetal strip serving as an electrode in an electrical circuit comprisingthe electrode and a counter-electrode immersed in the aqueouselectrodepositable coating composition, the composition being depositedonto one major surface of the metal strip as a substantially continuouscoating as electric current is passed between the electrodes; (3)conveying the metal strip from step (2) to a drying station located onthe coating line; (4) drying the electrodeposited coating as the metalstrip passes through the drying station; and (5) optionally, conveyingthe coated metal strip from step (4) to a recoiling station andrecoiling the coated metal strip.

DETAILED DESCRIPTION OF THE INVENTION

Other than in the operating examples, or where otherwise indicated, allnumbers expressing quantities of ingredients, reaction conditions and soforth used in the specification and claims are to be understood as beingmodified in all instances by the term “about.” Accordingly, unlessindicated to the contrary, the numerical parameters set forth in thefollowing specification and attached claims are approximations that mayvary depending upon the desired properties sought to be obtained by thepresent invention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should at least be construed in light of thenumber of reported significant digits and by applying ordinary roundingtechniques.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contain certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements.

Also, it should be understood that any numerical range recited herein isintended to include all sub-ranges subsumed therein. For example, arange of “1 to 10” is intended to include all sub-ranges between (andincluding) the recited minimum value of 1 and the recited maximum valueof 10, that is, having a minimum value equal to or greater than 1 and amaximum value of equal to or less than 10.

As discussed above, in one embodiment, the present invention provides aprocess for forming an electrodepositable coating on a pre-sheared,electroconductive, flat blank having two major surfaces and shearededges (hereinafter referred to as a “blank”). The blanks typically, butnot necessarily, are cut or “sheared” from coiled metal substrates priorto coating.

As used herein, by “flat” or “substantially flat” is meant substantiallyplanar in form, that is, a primarily level substrate lying in ageometric plane, which, as would be understood by one skilled in theart, can include slight bends, projections or depressions therein.

The metallic substrates, whether in the form of a coiled metal strip ora blank, which are used in the practice of the present invention caninclude ferrous metals and non-ferrous metals. Suitable ferrous metalsinclude iron, steel, and alloys thereof. Non-limiting examples of usefulsteel materials include cold-rolled steel, galvanized (zinc coated)steel, electrogalvanized steel, stainless steel, pickled steel,GALVANNEAL, GALVALUME, and GALVAN zinc-aluminum alloys coated uponsteel, and combinations thereof. Useful non-ferrous metals includealuminum, zinc, magnesium and alloys thereof. Combinations or compositesof ferrous and non-ferrous metals can also be used.

Before depositing coatings upon the surface of the metallic substrate,it is preferred to remove foreign matter from the metal surface bythoroughly cleaning and/or degreasing the substrate surface. As usedherein, the terms “deposited upon” and “provided upon” a substrate meandeposited or provided above or over but not necessarily adjacent to thesurface of the substrate. For example, a coating can be depositeddirectly upon the substrate or one or more other coatings can be appliedtherebetween.

The surface of the metallic substrate can be cleaned by physical orchemical means, such as mechanically abrading the surface or, as istypical, cleaning/degreasing with commercially available alkaline oracidic cleaning agents which are well known to those skilled in the art,such as sodium metasilicate and sodium hydroxide. Non-limiting examplesof suitable cleaning agents include CHEMKLEEN® 163 and CHEMKLEEN® 177phosphate cleaners, both of which are commercially available from PPGIndustries, Inc. of Pittsburgh, Pa.

Following the cleaning step, the surface of the metallic substrate maybe rinsed with water, typically deionized water, in order to remove anyresidue. Optionally, the metal surface can be rinsed with an aqueousacidic solution after cleaning with the alkaline cleaners. Examples ofrinse solutions include mild or strong acidic cleaners such as thedilute nitric acid solutions commercially available and conventionallyused in metal pretreatment processes. The metallic substrate can beair-dried using an air knife, by flashing off the water by briefexposure of the substrate to a high temperature or by passing thesubstrate between squeegee rolls.

Optionally, a phosphate-based pretreatment or conversion coating can beapplied to the metallic substrate. Suitable phosphate conversion coatingcompositions include those known in the art, such as zinc phosphate,optionally modified with nickel, iron, manganese, calcium, magnesium orcobalt. Useful phosphating compositions are described in U.S. Pat. Nos.4,793,867 and 5,588,989; 4,941,930; 5,238,506 and 5,653,790.

The coiled metal substrate can undergo cleaning and pretreatment stepsprior to coating or forming the blanks, or, alternatively, thepre-sheared blanks can undergo similar cleaning and pretreatment stepsprior to coating.

The pre-sheared blanks are loaded onto a conveyor mechanism, whichtypically is composed primarily of a non-conductive material, formovement throughout the coating line. The conveyor may be of anyconvenient type, such as, but not limited to, a belt conveyor, a chainconveyor a platform conveyor and the like.

With reference to FIG. 1, in step (1), the pre-sheared blanks areconveyed to the entrance of an electrodeposition bath tank (1) locatedon a coating line (A). The electrodeposition bath (1) contains anaqueous electrodeposition bath composition.

The electrodeposition bath composition useful in the methods of thepresent invention comprises a resinous phase dispersed in an aqueousmedium. The resinous phase includes a film-forming organic componentwhich can comprise an anionic electrodepositable coating composition,or, as is preferred, a cationic electrodepositable coating composition.The electrodepositable coating composition typically comprises an activehydrogen group-containing ionic resin and a curing agent havingfunctional groups reactive with the active hydrogens of the ionic resin.

As used herein, the term “reactive” refers to a functional group thatforms a covalent bond with another functional group under suitablereaction conditions.

Non-limiting examples of anionic electrodepositable coating compositionsinclude those comprising an ungelled, water-dispersibleelectrodepositable anionic film-forming resin. Examples of film-formingresins suitable for use in anionic electrodeposition coatingcompositions are base-solubilized, carboxylic acid containing polymers,such as the reaction product or adduct of a drying oil or semi-dryingfatty acid ester with a dicarboxylic acid or anhydride; and the reactionproduct of a fatty acid ester, unsaturated acid or anhydride and anyadditional unsaturated modifying materials which are further reactedwith polyol. Also suitable are the at least partially neutralizedinterpolymers of hydroxy-alkyl esters of unsaturated carboxylic acids,unsaturated carboxylic acid and at least one other ethylenicallyunsaturated monomer. Yet another suitable electrodepositable anionicresin comprises an alkyd-aminoplast vehicle, i.e., a vehicle containingan alkyd resin and an amine-aldehyde resin. Yet another anionicelectrodepositable resin composition comprises mixed esters of aresinous polyol. These compositions are described in detail in U.S. Pat.No. 3,749,657 at col. 9, lines 1 to 75 and col. 10, lines 1 to 13. Otheracid functional polymers can also be used such as phosphatizedpolyepoxide or phosphatized acrylic polymers as are well known to thoseskilled in the art.

By “ungelled” is meant that the polymer is substantially free ofcrosslinking and has an intrinsic viscosity when dissolved in a suitablesolvent. The intrinsic viscosity of a polymer is an indication of itsmolecular weight. A gelled polymer, on the other hand, since it is ofessentially infinitely high molecular weight, will have an intrinsicviscosity too high to measure.

With reference to the cationic resin, a wide variety of cationicpolymers are known and can be used in the compositions of the inventionso long as the polymers are “water dispersible,” i.e., adapted to besolubilized, dispersed or emulsified in water. The water dispersibleresin is cationic in nature, that is, the polymer contains cationicfunctional groups to impart a positive charge. Preferably, the cationicresin also contains active hydrogen groups.

Examples of cationic resins suitable include onium salt group-containingresins such as ternary sulfonium salt group-containing resins andquaternary phosphonium salt-group containing resins, for example, thosedescribed in U.S. Pat. Nos. 3,793,278 and 3,984,922, respectively. Othersuitable onium salt group-containing resins include quaternary ammoniumsalt group-containing resins, for example, those which are formed fromreacting an organic polyepoxide with a tertiary amine salt. Such resinsare described in U.S. Pat. Nos. 3,962,165; 3,975,346; and 4,001,101.Also suitable are the amine salt group-containing resins such as theacid-solubilized reaction products of polyepoxides and primary orsecondary amines such as those described in U.S. Pat. Nos. 3,663,389;3,984,299; 3,947,338 and 3,947,339.

Usually, the above-described salt group-containing resins describedabove are used in combination with a blocked isocyanate curing agent.The isocyanate can be fully blocked as described in the aforementionedU.S. Pat. No. 3,984,299 or the isocyanate can be partially blocked andreacted with the resin backbone such as is described in U.S. Pat. No.3,947,338.

Also, one-component compositions as described in U.S. Pat. No. 4,134,866and DE-OS No. 2,707,405 can be used as the cationic resin. Besides theepoxy-amine reaction products, resins can also be selected from cationicacrylic resins such as those described in U.S. Pat. Nos. 3,455,806 and3,928,157. Also, cationic resins which cure via transesterification suchas described in European Application No. 12463 can be used. Further,cationic compositions prepared from Mannich bases such as described inU.S. Pat. No. 4,134,932 can be used. Also useful in theelectrodepositable coating compositions of the present invention arethose positively charged resins which contain primary and/or secondaryamine groups. Such resins are described in U.S. Pat. Nos. 3,663,389;3,947,339; and 4,115,900. U.S. Pat. No. 3,947,339 describes apolyketimine derivative of a polyamine such as diethylenetriamine ortriethylenetetraamine with the excess polyamine vacuum stripped from thereaction mixture. Such products are described in U.S. Pat. Nos.3,663,389 and 4,116,900.

In one embodiment of the present invention, the cationic resins suitablefor inclusion in the electrodepositable coating compositions useful inthe methods of the present invention are onium salt group-containingacrylic resins.

The cationic resin described immediately above is typically present inthe electrodepositable coating compositions in amounts of 1 to 60 weightpercent, preferably 5 to 25 weight percent based on total weight of thecomposition.

As previously discussed, the electrodepositable coating compositionswhich are useful in the methods of the present invention typicallyfurther comprise a curing agent which contains functional groups whichare reactive with the active hydrogen groups of the ionic resin.

Aminoplast resins, which are the preferred curing agents for anionicelectrodeposition, are the condensation products of amines or amideswith aldehydes. Examples of suitable amine or amides are melamine,benzoguanamine, urea and similar compounds. Generally, the aldehydeemployed is formaldehyde, although products can be made from otheraldehydes such as acetaldehyde and furfural. The condensation productscontain methylol groups or similar alkylol groups depending on theparticular aldehyde employed. Preferably, these methylol groups areetherified by reaction with an alcohol. Various alcohols employedinclude monohydric alcohols containing from 1 to 4 carbon atoms such asmethanol, ethanol, isopropanol, and n-butanol, with methanol beingpreferred. Aminoplast resins are commercially available from AmericanCyanamid Co. under the trademark CYMEL® and from Monsanto Chemical Co.under the trademark RESIMENE®.

The aminoplast curing agents are typically utilized in conjunction withthe active hydrogen containing anionic electrodepositable resin inamounts ranging from about 5 percent to about 60 percent by weight,preferably from about 20 percent to about 40 percent by weight, thepercentages based on the total weight of the resin solids in theelectrodeposition bath.

The curing agents most often employed for cationic electrodepositablecoating compositions are blocked organic polyisocyanates. Thepolyisocyanates can be fully blocked as described in U.S. Pat. No.3,984,299 column 1 lines 1 to 68, column 2 and column 3 lines 1 to 15,or partially blocked and reacted with the polymer backbone as describedin U.S. Pat. No. 3,947,338 column 2 lines 65 to 68, column 3 and column4 lines 1 to 30. By “blocked” is meant that the isocyanate groups havebeen reacted with a compound so that the resultant blocked isocyanategroup is stable to active hydrogens at ambient temperature but reactivewith active hydrogens in the film forming polymer at elevatedtemperatures, usually between 90° C. and 200° C.

Suitable polyisocyanates include aromatic and aliphatic polyisocyanates,including cycloaliphatic polyisocyanates and representative examplesinclude diphenylmethane-4,4′-diisocyanate (MDI), 2,4- or 2,6-toluenediisocyanate (TDI), including mixtures thereof, p-phenylenediisocyanate, tetramethylene and hexamethylene diisocyanates,dicyclohexylmethane-4,4′-diisocyanate, isophorone diisocyanate, mixturesof phenylmethane-4,4′-diisocyanate and polymethylenepolyphenylisocyanate. Higher polyisocyanates such as triisocyanates canbe used. An example would includetriphenylmethane-4,4′,4″-triisocyanate. Isocyanate prepolymers withpolyols such as neopentyl glycol and trimethylolpropane and withpolymeric polyols such as polycaprolactone diols and triols (NCO/OHequivalent ratio greater than 1) can also be used.

The polyisocyanate curing agents are typically utilized in conjunctionwith the cationic resin in amounts ranging from 1 weight percent to 65weight percent, preferably from 5 weight percent to 45 weight percent,based on the weight of the total resin solids present composition.

The aqueous compositions of the present invention are in the form of anaqueous dispersion. The term “dispersion” is believed to be a two-phasetransparent, translucent or opaque resinous system in which the resin isin the dispersed phase and the water is in the continuous phase. Theaverage particle size of the resinous phase is generally less than 1.0and usually less than 0.5 microns, preferably less than 0.15 micron.

The concentration of the resinous phase in the aqueous medium is atleast 1 and usually from about 2 to about 60 percent by weight based ontotal weight of the aqueous dispersion. When the compositions of thepresent invention are in the form of resin concentrates, they generallyhave a resin solids content of about 20 to about 60 percent by weightbased on weight of the aqueous dispersion.

Electrodeposition baths useful in the methods of the present inventionare typically supplied as two components: (1) a clear resin feed, whichincludes generally the active hydrogen-containing ionicelectrodepositable resin, i.e., the main film-forming polymer, thecuring agent, and any additional water-dispersible, non-pigmentedcomponents; and (2) a pigment paste, which generally includes one ormore pigments, a water-dispersible grind resin which can be the same ordifferent from the main-film forming polymer, and, optionally, additivessuch as wetting or dispersing aids. Electrodeposition bath components(1) and (2) are dispersed in an aqueous medium which comprises waterand, usually, coalescing solvents.

The electrodeposition bath of the present invention has a resin solidscontent usually within the range of about 5 to 25 percent by weightbased on total weight of the electrodeposition bath.

As aforementioned, besides water, the aqueous medium may contain acoalescing solvent. Useful coalescing solvents include hydrocarbons,alcohols, esters, ethers and ketones. The preferred coalescing solventsinclude alcohols, polyols and ketones. Specific coalescing solventsinclude isopropanol, butanol, 2-ethylhexanol, isophorone,2-methoxypentanone, ethylene and propylene glycol and the monoethyl,monobutyl and monohexyl ethers of ethylene glycol. The amount ofcoalescing solvent is generally between about 0.01 and 25 percent andwhen used, typically from about 0.05 to about 5 percent by weight basedon total weight of the aqueous medium.

As discussed above, a pigment composition and, if desired, variousadditives such as surfactants, wetting agents or catalyst can beincluded in the dispersion. The pigment composition may be of theconventional type comprising pigments, for example, iron oxides,strontium chromate, carbon black, coal dust, titanium dioxide, talc,barium sulfate, as well as color pigments such as cadmium yellow,cadmium red, chromium yellow and the like.

The pigment content of the dispersion is usually expressed as apigment-to-resin ratio. In the practice of the invention, when pigmentis employed, the pigment-to-resin ratio is usually within the range ofabout 0.02 to 1:1. The other additives mentioned above are usually inthe dispersion in amounts of about 0.01 to 3 percent by weight based onweight of resin solids.

In step (2) the aqueous electrodepositable coating composition isapplied to both major surfaces and the sheared edges of the blank as theblank passes through the electrodeposition bath. In the process of thepresent invention, the blank serves as an electrode, preferably thecathode, in an electrical circuit comprising the electrode and acounter-electrode which are immersed in the aqueous electrodepositablecoating composition. The composition is deposited onto both majorsurfaces and the sheared edges of the blank as a substantiallycontinuous coating as electric current is passed between the twoelectrodes.

In the process of applying the electrodepositable coating, the aqueousdispersion of the electrodepositable composition is placed in contactwith an electrically conductive anode and cathode. Upon passage of anelectric current between the anode and cathode, an adherent film of theelectrodepositable composition will deposit in a substantiallycontinuous manner on the substrate serving as either the anode or thecathode depending on whether the composition is anionically orcationically electrodepositable. Electrodeposition is usually carriedout at a constant voltage ranging from 1 volt to 7,000 volts, andtypically between 50 and 500 volts. Current density is usually betweenabout 1.0 ampere and 15 amperes per square foot (10.8 to 161.5 amperesper square meter).

In step (3) the coated blank is conveyed from the electrodeposition bath(1) to a first drying station (2) located on the coating line (A), andin step (4) the electrodeposited coating is dried as it passes throughthe first drying station (2).

As used herein the term “dried” is intended to include both drying andcuring. In one embodiment, the electrodeposited coating is dried bydriving substantially all the solvent and/or water from the coatingeither by evaporation at ambient temperature or by forced drying atelevated temperatures (for example 150° F. to 800° F. (82° C. to 426°C.)). The term “dried” is also intended to include “cured” as byexposing the electrocoated substrate to thermal conditions sufficient toeffectuate crosslinking of the co-reactive film components.

Also, as used herein, the term “cure” as used in connection with acomposition, e.g., “a cured composition,” shall mean that anycrosslinkable or co-reactive components of the composition are at leastpartially crosslinked or co-reacted. In certain embodiments of thepresent invention, the crosslink density of the crosslinkablecomponents, i.e., the degree of crosslinking, ranges from 5% to 100% ofcomplete crosslinking. In other embodiments, the crosslink densityranges from 35% to 85% of full crosslinking. In other embodiments, thecrosslink density ranges from 50% to 85% of full crosslinking. Oneskilled in the art will understand that the presence and degree ofcrosslinking, i.e., the crosslink density, can be determined by avariety of methods, such as dynamic mechanical thermal analysis (DMTA)using a Polymer Laboratories MK III DMTA analyzer conducted undernitrogen. This method determines the glass transition temperature andcrosslink density of free films of coatings or polymers. These physicalproperties of a cured material are related to the structure of thecrosslinked network.

According to this method, the length, width, and thickness of a sampleto be analyzed are first measured, the sample is tightly mounted to thePolymer Laboratories MK III apparatus, and the dimensional measurementsare entered into the apparatus. A thermal scan is run at a heating rateof 3° C./min, a frequency of 1 Hz, a strain of 120%, and a static forceof 0.01N, and sample measurements occur every two seconds. The mode ofdeformation, glass transition temperature, and crosslink density of thesample can be determined according to this method. Higher crosslinkdensity values indicate a higher degree of crosslinking in the coating.

Generally, the electrodepositable coating compositions which are usefulin the methods of the present invention are applied under conditionssuch that a substantially continuous coating having a driedfilm-thickness ranging from 0.1 to 1.8 mils (2.54 to 45.72 micrometers),usually from 0.15 to 1.6 mils (30.48 to 40.64 micrometers) is formedupon both major surfaces of the metal blank.

In one embodiment of the present invention, after the coating has beenapplied by electrodeposition, it is cured, usually by baking, atelevated temperatures ranging from 90° C. to 430° C. for a periodranging from 60 to 1200 seconds. The first drying station (2) can be anyof a variety of curing ovens, both electric and gas powered, that arewell known in the art for use on coating lines. Alternatively, thecoating can be cured using infrared curing techniques as are well knownin the art, typically for a period ranging from 45 to 240 seconds or atime sufficient to obtain a peak metal temperature ranging from 300° to700° F. (148.9° to 371.1° C.).

It should be understood that the electrocoating applied by the methoddescribed immediately above can be an electrocoating primer suitable asa primary coating for subsequent application of a non-electrophoreticcoating as described in detail below. Alternatively, the electrocoatingcan be an appearance-enhancing electrodeposited top coating. In the caseof a primer coating, the electrodepositable coating composition is suchthat a substantially continuous primer coating having a driedfilm-thickness ranging from 0.1 to 0.4 mils (2.54 to 81.28 micrometers),usually from 0.15 to 2.5 mils (30.48 to 50.8 micrometers) is formed uponboth major surfaces of the metal blank. In the case of anappearance-enhancing top coat, the electrodepositable coatingcomposition is applied such that a substantially continuous top coatinghaving a dried film-thickness ranging from 0.8 to 1.8 mils (20.32 to45.72 micrometers), usually from 1.0 to 1.6 mils (25.4 to 40.6micrometers) is formed upon both major surfaces of the metal blank.

As mentioned above, the method described immediately above can furthercomprise the steps of conveying the electrocoated blanks to a secondcoating station (4) located on the coating line (A); applying a secondnon-electrophoretic coating composition to at least one major surface ofthe blank as it passes through the coating station (4) to form acontinuous coating thereon; conveying the coated blank to a seconddrying station (5) located on the coating line (A); and drying thecoating as it passes through the second drying station (5).

The non-electrophoretic coating composition can be any of a variety ofcoating compositions well known in the art and the specific compositionutilized is generally dependent upon the final appearance andperformance properties dictated by the end use of the coated substrate.For example, the non-electrophoretic coating composition can be a liquidcoating composition or in solid particulate form, e.g., a powder coatingcomposition.

The second non-electrophoretic coating composition when in liquid formcan be applied by any of the conventional liquid coating applicationtechniques well known in the art as discussed below. Typically when thesecond non-electrophoretic coating composition is in liquid form, thesecond coating station (4) comprises a spray booth for spray applicationof the second coating composition or, alternatively, a roll-coatingapparatus for roll-application of the second coating composition.Suitable spray booths as are well known in the art can be configured toaccommodate conventional as well as electrostatic spray apparatus.

Likewise, when the second non-electrophoretic coating composition is apowder coating composition, the second coating station (4) comprises asuitably equipped powder spray booth for electrostatic spray applicationof the powder composition.

Liquid coating compositions suitable for use as the non-electrophoreticcoating composition in the method of the present invention can be any ofthe wide variety of liquid film-forming compositions known in the art.For example, suitable liquid coating compositions typically comprise afilm-forming composition which includes a resinous binder system and,optionally, one or more pigments to serve as a colorant. The resinousbinder system typically comprises a film-forming polymer. Depending uponthe functionality of the film-forming polymers, the film-formingcompositions can also contain one or more crosslinking agents reactivewith the functionality of the polymer.

Non-limiting examples of film-forming polymers having reactivefunctional groups which are useful in the liquid coating compositionsinclude those selected from acrylic, polyester, polyurethane,polyepoxide and polyether polymers. As mentioned above, the film-formingpolymer typically comprises reactive functional groups, for example,hydroxyl, epoxy, carboxyl, isocyanate and carbamate functional groupsor, if desired, a combination thereof. Hydroxyl group-containing acrylicpolymers and/or polyester polymers are often employed.

Suitable functional group-containing acrylic polymers include copolymersprepared from one or more alkyl esters of acrylic acid or methacrylicacid and, optionally, one or more other polymerizable ethylenicallyunsaturated monomers. Suitable alkyl esters of acrylic or methacrylicacid include methyl (meth)acrylate, ethyl (meth)acrylate, butyl(meth)acrylate, and 2-ethylhexyl (meth)acrylate. As used herein, theterm “(meth)acrylate” and like terms is intended to include bothmethacrylates and acrylates. Ethylenically unsaturated carboxylic acidfunctional monomers, for example acrylic acid and/or methacrylic acid,can also be used when a carboxylic acid functional acrylic polymer isdesired. Non-limiting examples of other polymerizable ethylenicallyunsaturated monomers include vinyl aromatic compounds, such as styreneand vinyl toluene; nitriles, such as acrylonitrile andmethacrylonitrile; vinyl and vinylidene halides, such as vinyl chlorideand vinylidene fluoride and vinyl esters, such as vinyl acetate.

In one embodiment of the present invention, the acrylic polymers containhydroxyl functionality which can be incorporated into the acrylicpolymer through the use of one or more hydroxyl functional monomers suchas hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethylmethacrylate and hydroxypropyl methacrylate which may be copolymerizedwith the other acrylic monomers mentioned above.

The acrylic polymer also can be prepared from ethylenically unsaturated,beta-hydroxy ester functional monomers. Such monomers are derived fromthe reaction of an ethylenically unsaturated acid functional monomer,such as monocarboxylic acids, for example, acrylic acid, and an epoxycompound which does not participate in the free radical initiatedpolymerization with the unsaturated acid monomer. Examples of such epoxycompounds are glycidyl ethers and esters. Suitable glycidyl ethersinclude glycidyl ethers of alcohols and phenols, such as butyl glycidylether, octyl glycidyl ether, phenyl glycidyl ether and the like.Suitable glycidyl esters include those which are commercially availablefrom Shell Chemical Company under the tradename CARDURA® E; and fromExxon Chemical Company under the tradename GLYDEXX®-10.

Alternatively, the beta-hydroxy ester functional monomers are preparedfrom an ethylenically unsaturated, epoxy functional monomer, for exampleglycidyl methacrylate and allyl glycidyl ether, and a saturatedcarboxylic acid, such as a saturated monocarboxylic acid, for example,isostearic acid.

The acrylic polymer is typically prepared by solution polymerizationtechniques in the presence of suitable initiators such as organicperoxides or azo compounds, for example, benzoyl peroxide orN,N-azobis(isobutyronitrile). The polymerization can be carried out inan organic solution in which the monomers are soluble by techniquesconventional in the art.

Pendent and/or terminal carbamate functional groups can be incorporatedinto the acrylic polymer by copolymerizing the acrylic monomer with acarbamate functional vinyl monomer, such as a carbamate functional alkylester of methacrylic acid. These carbamate functional alkyl esters areprepared by reacting, for example, a hydroxyalkyl carbamate, such as thereaction product of ammonia and ethylene carbonate or propylenecarbonate, with methacrylic anhydride. Other carbamate functional vinylmonomers can include the reaction product of hydroxyethyl methacrylate,isophorone diisocyanate and hydroxypropyl carbamate. Still othercarbamate functional vinyl monomers may be used, such as the reactionproduct of isocyanic acid (HNCO) with a hydroxyl functional acrylic ormethacrylic monomer such as hydroxyethyl acrylate, and those carbamatefunctional vinyl monomers described in U.S. Pat. No. 3,479,328.

Carbamate groups can also be incorporated into the acrylic polymer by a“transcarbamoylation” reaction in which a hydroxyl functional acrylicpolymer is reacted with a low molecular weight carbamate derived from analcohol or a glycol ether. The carbamate groups exchange with thehydroxyl groups yielding the carbamate functional acrylic polymer andthe original alcohol or glycol ether.

The low molecular weight carbamate functional material derived from analcohol or glycol ether is first prepared by reacting the alcohol orglycol ether with urea in the presence of a catalyst such as butylstannoic acid. Suitable alcohols include lower molecular weightaliphatic, cycloaliphatic and aromatic alcohols, such as methanol,ethanol, propanol, butanol, cyclohexanol, 2-ethylhexanol and3-methylbutanol. Suitable glycol ethers include ethylene glycol methylether and propylene glycol methyl ether. Propylene glycol methyl etheris typically employed.

Also, hydroxyl functional acrylic polymers can be reacted with isocyanicacid yielding pendent carbamate groups. Note that the production ofisocyanic acid is disclosed in U.S. Pat. No. 4,364,913. Likewise,hydroxyl functional acrylic polymers can be reacted with urea to give anacrylic polymer with pendent carbamate groups.

Epoxide functional acrylic polymers are typically prepared bypolymerizing one or more epoxide functional ethylenically unsaturatedmonomers, e.g., glycidyl (meth)acrylate, with one or more ethylenicallyunsaturated monomers that are free of epoxide functionality, e.g.,methyl (meth)acrylate, isobornyl (meth)acrylate, butyl (meth)acrylateand styrene. Examples of epoxide functional ethylenically unsaturatedmonomers that may be used in the preparation of epoxide functionalacrylic polymers include, but are not limited to, glycidyl(meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate,2-(3,4-epoxycyclohexyl)ethyl (meth)acrylate and allyl glycidyl ether.Examples of ethylenically unsaturated monomers that are free of epoxidefunctionality include those described above as well as those describedin U.S. Pat. No. 5,407,707 at column 2, lines 17 through 56, whichdisclosure is incorporated herein by reference. In one embodiment of thepresent invention, the epoxide functional acrylic polymer is preparedfrom a majority of (meth)acrylate monomers.

Isocyanate functional groups can be incorporated into the acrylicpolymer, for example, by reacting an acrylic polyol, such as thosedescribed above, with a polyisocyanate using reactant ratios andreaction conditions well known in the art to ensure the desiredisocyanate functional groups. Examples of suitable polyisocyanates arethose described in U.S. Pat. No. 4,046,729 at column 5, line 26 tocolumn 6, line 28, hereby incorporated by reference

The functional group-containing acrylic polymer typically has a Mnranging from 500 to 30,000 and often from 1000 to 5000. If carbamatefunctional, the acrylic polymer typically has a calculated carbamateequivalent weight typically within the range of 15 to 150, and usuallyless than 50, based on equivalents of reactive carbamate groups.

Non-limiting examples of functional group-containing polyester polymerssuitable for use in the liquid film-forming compositions can includelinear or branched polyesters having hydroxyl, carboxyl and/or carbamatefunctionality. Such polyester polymers are generally prepared by thepolyesterification of a polycarboxylic acid or anhydride thereof withpolyols and/or an epoxide using techniques known to those skilled in theart. Usually, the polycarboxylic acids and polyols are aliphatic oraromatic dibasic acids and diols. Transesterification of polycarboxylicacid esters using conventional techniques is also possible.

The polyols which usually are employed in making the polyester (or thepolyurethane polymer, as described below) include alkylene glycols, suchas ethylene glycol and other diols, such as neopentyl glycol,hydrogenated Bisphenol A, cyclohexanediol, butyl ethyl propane diol,trimethyl pentane diol, cyclohexanedimethanol, caprolactonediol, forexample, the reaction product of epsilon-caprolactone and ethyleneglycol, hydroxy-alkylated bisphenols, polyether glycols, for example,poly(oxytetramethylene) glycol and the like. Polyols of higherfunctionality may also be used. Examples include trimethylolpropane,trimethylolethane, pentaerythritol, tris-hydroxyethylisocyanurate andthe like. Branched polyols, such as trimethylolpropane, are typicallyemployed in the preparation of the polyester.

The acid component used to prepare the polyester polymer can include,primarily, monomeric carboxylic acids or anhydrides thereof having 2 to18 carbon atoms per molecule. Among the acids which are useful arecycloaliphatic acids and anhydrides, such as phthalic acid, isophthalicacid, terephthalic acid, tetrahydrophthalic acid, hexahydrophthalicacid, methylhexahydrophthalic acid, 1,3-cyclohexane dicarboxylic acidand 1,4-cyclohexane dicarboxylic acid. Other suitable acids includeadipic acid, azelaic acid, sebacic acid, maleic acid, glutaric acid,decanoic diacid, dodecanoic diacid and other dicarboxylic acids ofvarious types. The polyester may include minor amounts of monobasicacids such as benzoic acid, stearic acid, acetic acid and oleic acid.Also, there may be employed higher carboxylic acids, such as trimelliticacid and tricarballylic acid. Where acids are referred to above, it isunderstood that anhydrides thereof which exist may be used in place ofthe acid. Also, lower alkyl esters of diacids such as dimethyl glutarateand dimethyl terephthalate can be used. Because it is readily availableand low in cost, terephthalic acid is often employed.

Pendent and/or terminal carbamate functional groups may be incorporatedinto the polyester by first forming a hydroxyalkyl carbamate which canbe reacted with the polyacids and polyols used in forming the polyester.The hydroxyalkyl carbamate is condensed with acid functionality on thepolyester yielding carbamate functionality. Carbamate functional groupsmay also be incorporated into the polyester by reacting a hydroxylfunctional polyester with a low molecular weight carbamate functionalmaterial via a transcarbamoylation process similar to the one describedabove in connection with the incorporation of carbamate groups into theacrylic polymers or by reacting isocyanic acid with a hydroxylfunctional polyester.

Epoxide functional polyesters can be prepared by art-recognized methods,which typically include first preparing a hydroxy functional polyesterthat is then reacted with epichlorohydrin. Polyesters having hydroxyfunctionality may be prepared by art-recognized methods, which includereacting carboxylic acids (and/or esters thereof) having acid (or ester)functionalities of at least two (2), and polyols having hydroxyfunctionalities of at least two (2). As is known to those of ordinaryskill in the art, the molar equivalents ratio of carboxylic acid groupsto hydroxy groups of the reactants is selected such that the resultingpolyester has hydroxy functionality and the desired molecular weight.

Isocyanate functional groups can be incorporated into the polyesterpolymer by reacting a polyester polyol such as those described abovewith a polyisocyanate using reactant ratios and reaction conditions suchas those well known in the art. Examples of suitable polyisocyanatesinclude those described above with reference to acrylic polymers havingisocyanate functional groups.

The functional group-containing polyester polymer typically has a Mnranging from 500 to 30,000, usually about 1000 to 5000. If carbamatefunctional, the polyester polymer typically has a calculated carbamateequivalent weight within the range of 15 to 150, usually 20 to 75, basedon equivalents of reactive pendent or terminal carbamate groups.

Non-limiting examples of suitable polyurethane polymers having pendentand/or terminal hydroxyl and/or carbamate functional groups include thepolymeric reaction products of polyols, which are prepared by reactingthe polyester polyols or acrylic polyols, such as those mentioned above,with a polyisocyanate such that the OH/NCO equivalent ratio is greaterthan 1:1 such that free hydroxyl groups are present in the product. Suchreactions employ typical conditions for urethane formation, for example,temperatures of 60° C. to 90° C. and up to ambient pressure, as known tothose skilled in the art.

The organic polyisocyanates which can be used to prepare the functionalgroup-containing polyurethane polymer include aliphatic or aromaticpolyisocyanates or a mixture of the two. Diisocyanates are oftenemployed, although higher polyisocyanates can be used in place of or incombination with diisocyanates.

Examples of suitable aromatic diisocyanates include 4,4′-diphenylmethanediisocyanate and toluene diisocyanate. Examples of suitable aliphaticdiisocyanates include straight chain aliphatic diisocyanates, such as1,6-hexamethylene diisocyanate. Also, cycloaliphatic diisocyanates canbe employed. Examples include isophorone diisocyanate and4,4′-methylene-bis-(cyclohexyl isocyanate). Examples of suitable higherpolyisocyanates include 1,2,4-benzene triisocyanate and polymethylenepolyphenyl isocyanate.

Terminal and/or pendent carbamate functional groups can be incorporatedinto the polyurethane by reacting a polyisocyanate with a polyesterpolyol containing the terminal/pendent carbamate groups. Alternatively,carbamate functional groups can be incorporated into the polyurethane byreacting a polyisocyanate with a polyester polyol and a hydroxyalkylcarbamate or isocyanic acid as separate reactants. Carbamate functionalgroups can also be incorporated into the polyurethane by reacting ahydroxyl functional polyurethane with a low molecular weight carbamatefunctional material via a transcarbamoylation process similar to the onedescribed above in connection with the incorporation of carbamate groupsinto the acrylic polymer.

Isocyanate functional polyurethane polymers can be prepared by reactingpolyurethane polyols such as those described above with polyisocyanatessuch as those described above with reference to the polyurethanepolyols. The hydroxyl/isocyanate equivalent ratio is adjusted andreaction conditions selected to obtain the desired isocyanate functionalgroups.

The polyurethane polymers generally have a Mn ranging from 500 to 20,000and typically from 1000 to 5000. If carbamate functional, thepolyurethane polymer typically has a carbamate equivalent weight withinthe range of 15 to 150, often within the range of 20 to 75, based onequivalents of reactive pendent or terminal carbamate groups.

Functional group-containing polyether polymer also can be used as afilm-forming polymer in the liquid film-forming compositions. Suitablehydroxyl and/or carbamate functional polyether polymers can be preparedby reacting a polyether polyol with urea under reaction conditions wellknown to those skilled in the art. Most often, the polyether polymer isprepared by a transcarbamoylation reaction similar to the reactiondescribed above in connection with the incorporation of carbamate groupsinto the acrylic polymers.

Examples of polyether polyols are polyalkylene ether polyols whichinclude those having the following structural formulae (I) and (II):

where the substituent R₁ is hydrogen or lower alkyl containing from 1 to5 carbon atoms including mixed substituents, n is typically from 2 to 6,and m is from 8 to 100 or higher. Note that the hydroxyl groups, asshown in structures (II) and (III) above, are terminal to the molecules.Included are poly(oxytetramethylene) glycols, poly(oxytetraethylene)glycols, poly(oxy-1,2-propylene) glycols and poly(oxy-1,2-butylene)glycols.

Also useful are polyether polyols formed from oxyalkylation of variouspolyols, for example, diols, such as ethylene glycol, 1,6-hexanediol,Bisphenol A and the like, or other higher polyols, such astrimethylolpropane, pentaerythritol and the like. Polyols of higherfunctionality which can be utilized as indicated can be made, forinstance, by oxyalkylation of compounds, such as sucrose or sorbitol.One commonly utilized oxyalkylation method is reaction of a polyol withan alkylene oxide, for example, propylene or ethylene oxide, in thepresence of a conventional acidic or basic catalyst as known to thoseskilled in the art. Typical oxyalkylation reaction conditions may beemployed. Typically employed polyethers include those sold under thenames TERATHANE® and TERACOL®, available from E. I. Du Pont de Nemoursand Company, Inc. and POLYMEG®, available from Q O Chemicals, Inc., asubsidiary of Great Lakes Chemical Corp.

Epoxide functional polyethers can be prepared from a hydroxy functionalmonomer, e.g., a diol, and an epoxide functional monomer, and/or amonomer having both hydroxy and epoxide functionality. Suitable epoxidefunctional polyethers include, but are not limited to, those based on4,4′-isopropylidenediphenol (Bisphenol A), a specific example of whichis EPON® RESIN 2002 available commercially from Shell Chemicals.

Suitable functional group-containing polyether polymers generally have anumber average molecular weight (Mn) ranging from 500 to 30,000 andusually from 1000 to 5000. If carbamate functional, the polyetherpolymers have a carbamate equivalent weight of within the range of 15 to150, typically 25 to 75, based on equivalents of reactive pendent and/orterminal carbamate groups and the solids of the polyether polymer.

It should be understood that the carbamate functional group-containingpolymers typically contain residual hydroxyl functional groups whichprovide additional crosslinking sites. When this is the case, thecarbamate functional group-containing polymer (a) generally has aresidual hydroxyl value ranging from 10 to 150, usually from 10 to 100;and typically from 10 to 60 (mg KOH per gram).

The crosslinking agent can be any of the crosslinking agents well knownin the coatings art, provided that the crosslinking agent has functionalgroups which are reactive with the functional groups of the film-formingpolymer. Suitable crosslinking agents can include aminoplast resins,polycarboxylic acids, polyisocyanates, for example, the isocyanatesdescribed above, and mixtures thereof.

The blocked isocyanates suitable for use as the crosslinking agent inthe liquid film-forming compositions are known compounds and can beobtained from commercial sources or may be prepared according topublished procedures. Upon being heated to cure the powder coatingcompositions, the isocyanates are unblocked and the isocyanate groupsbecome available to react with the functional groups of the polymer.

Any suitable aliphatic, cycloaliphatic or aromatic alkyl monoalcoholknown to those skilled in the art can be used as a blocking agent forthe isocyanate. Other suitable blocking agents include oximes andlactams. Non-limiting examples of suitable blocked isocyanate curingagents include those based on isophorone diisocyanate blocked withε-caprolactam; toluene 2,4-toluene diisocyanate blocked withε-caprolactam; or phenol-blocked hexamethylene diisocyanate. The blockedisocyanates mentioned immediately above are described in detail in U.S.Pat. No. 4,988,793 at column 3, lines 1 to 36.

Conventional aminoplast crosslinkers, including phenoplast resins can beused as the crosslinking agent in conjunction with hydroxyl and/orcarboxyl group-containing polymers. Aminoplast resins typically are thecondensation products of the reaction of formaldehyde with an amine oran amide. Most often the amines or amides are melamine, urea orbenzoguanamine. Condensates with other amines and amides can beemployed, for example, aldehyde condensates or diazines, triazoles,guanidines, guanamines and alkyl and aryl di-substituted derivatives ofsuch compounds including alkyl and aryl-substituted ureas and alkyl andaryl-substituted melamines and benzoguanamines. While the aldehyde mostoften used is formaldehyde, other aldehydes such a sacetaldehyde,crotonaldehyde, benzaldehyde and furfuryl can be used. The aminoplastcontains methylol or similar alkylol groups and often at least a portionof these groups are tehreified by reaction with an alcohol, for example,methanol, ethanol, butanol and mixtures thereof. Non-limiting examplesof suitable aminoplast resins include those discussed above.

Epoxide-reactive crosslinking agents can be used in coating compositionscomprising an epoxide functional polymer. The epoxide-reactivecrosslinking agents can comprise functional groups selected fromhydroxyl, thiol, primary amines, secondary amines, acid (e.g. carboxylicacid) and mixtures thereof. Typically, the epoxide reactive curing agenthas carboxylic acid groups.

One or more beta-hydroxyalkylamide crosslinking agents may be present inthe coating compositions comprising carboxylic acid functional polymer.The beta-hydroxyalkylamide crosslinking agent can be represented by thefollowing general formula IV:

for which R₁ is as described above, G is a chemical bond or monovalentor polyvalent organic radical derived from saturated, unsaturated oraromatic hydrocarbon radicals including substituted hydrocarbon radicalscontaining from 2 to 20 carbon atoms, m equals 1 or 2, p equals 0 to 2,and m+p is at least 2. Typically, G is an alkylene radical —(CH₂)_(x)—where x is equal to 2 to 12, often 4 to 10; m is equal to 1 to 2, p isequal to 0 to 2, and m+p is at least 2, typically greater than 2, andusually within the range from greater than 2 up to and including 4.

The beta-hydroxyalkylamide curing agent represented by general formula(IV) can be prepared by art recognized methods, as described in U.S.Pat. No. 4,937,288 at column 7, lines 6 through 16, which disclosure isincorporated herein by reference.

The crosslinking agent generally can be present in the liquid coatingcompositions in an amount ranging from 5 to 90 percent by weight, isoften present in an amount ranging from 5 to 50 percent by weight, andtypically 5 to 25 percent by weight, where weight percentages are basedon the weight of total resin solids present in the film-formingcomposition.

If desired, the liquid coating compositions also can include one or moreadjuvant curing agents. The adjuvant curing agent can be any compoundhaving functional groups reactive with the functional groups of thepolymer or the crosslinking agent described above. Non-limiting examplesof suitable adjuvant curing agents include any of the polyisocyanates,e.g., blocked isocyanates, and aminoplast resins discussed above. Whenemployed, the adjuvant curing agent generally is present in the liquidcoating compositions in an amount ranging from 5 to 10 percent byweight, usually from 5 to 20 percent by weight, often from 5 to 30percent by weight, and typically from 5 to 50 percent by weight based onthe total weight of the coating composition.

Also suitable for use as an adjuvant curing agent in the liquid coatingcompositions are triazine compounds, such as the tricarbamoyl triazinecompounds described in detail in U.S. Pat. No. 5,084,541. When used, thetriazine curing agent is typically present in the powder coatingcomposition of the present invention in an amount ranging up to about 20percent by weight, and can be present in an amount ranging from 1 to 20percent by weight, where percent by weight is based on the total weightof the powder coating composition.

Mixtures of the above-described crosslinking/curing agents also can beused advantageously in the liquid coating compositions of the presentinvention.

Also, it should be understood that for purposes of the presentinvention, the curable liquid coating compositions which contain anepoxy group-containing polymer typically also include anepoxide-reactive crosslinking agent, most often an acid functionalcrosslinking agent such as those described above. Typically, a secondaryhydroxyl group is generated upon reaction of each epoxy functional groupwith a functional group of the epoxide-reactive crosslinking agent.These secondary hydroxyl groups are then available for reaction with ahydroxyl-reactive adjuvant crosslinking agent such as anaminoplast-based crosslinking agent or a blocked isocyanate crosslinkingagent.

In one embodiment of the present invention, the non-electrophoreticcoating composition comprises a liquid film-forming compositioncomprising a hydroxyl functional group-containing polyester polymer inconjunction with an aminoplast crosslinking agent.

Suitable resinous binder systems can include organic solvent-basedmaterials, for example, those described in U.S. Pat. No. 4,220,679, aswell as water-based coating compositions, for example, those describedin U.S. Pat. Nos. 4,403,003; 4,147,679; and 5,071,904.

Additionally, the liquid non-electrophoretic coating compositions cancontain pigments of various types as colorants. Suitable metallicpigments include aluminum flake, bronze flake, copper flake and thelike. Other examples of suitable pigments include mica, iron oxides,lead oxides, carbon black, titanium dioxide, talc, as well as a varietyof color pigments.

Other optional ingredients include those which are well known in the artof surface coatings and include inorganic microparticles such as silica,for enhanced scratch and mar resistance, surfactants, flow controlagents, thixotropic agents, fillers, anti-gassing agents, organicco-solvents, catalysts and other suitable adjuvants.

As mentioned above, the liquid film-forming compositions can be appliedby any of the conventional coating techniques, such as brushing,spraying, dipping or flowing, but they are most often spray-applied. Theusual spray techniques and equipment for air spraying, airless sprayingand electrostatic spraying can be used.

The liquid film-forming compositions are typically applied such that acured coating having a film thickness ranging from 0.5 to 4 mils (12.5to 100 micrometers) is formed on at least one major surface of theelectrocoated blank as it passes through the coating station (4).

Powder coating compositions suitable for use as the second,non-electrophoretic coating composition in the method of the presentinvention can be any of the wide variety of powder coating compositionsknown in the art. Suitable powder coating compositions comprise aresinous binder system which typically is based on a solid particulatemixture of a functional group-containing film-forming polymer and asuitable crosslinking agent reactive with the functionality of thepolymer.

Examples of curable powder coating compositions useful in the method ofthe present invention include, but are not limited to, powder coatingcompositions comprising epoxide functional polymer and epoxide reactivecrosslinking agent, for example as described in U.S. Pat. Nos.5,407,707, 5,663,240 and 5,710,214; powder coating compositionscomprising carboxylic acid functional polymer and beta-hydroxyalkylamidefunctional crosslinking agent, for example as described in U.S. Pat.Nos. 4,801,680, 4,889,890, 4,937,288, 5,098,955, 5,202,382 and5,214,101; and powder coating compositions comprising hydroxy functionalpolymer and capped isocyanate functional crosslinking agent, for exampleas described U.S. Pat. Nos. 4,997,900, 5,439,896, 5,508,337, 5,510,444,5,554,692, 5,621,064 and 5,777,061. The disclosures of these citedUnited States patents are incorporated herein by reference in theirentirety.

As used herein and in the claims, by “polymer,” e.g., epoxide functionalpolymer, is meant oligomeric and/or polymeric species, and homopolymersand/or copolymers.

Typical drying (or curing) temperatures of suitable liquid coatingcompositions range from 140° C. to 260° C. (300° F. to 500° F.). Typicalcuring temperatures for powder coating compositions can range from 140°C. to 430° C. (300° F. to 800° F.). The second drying station (5) cancomprise any suitable coating line drying or curing oven as are wellknown in the art, as well as infrared curing means, as discussed abovewith reference to the first drying station (2).

Moreover, it should be understood that the non-electrophoretic coatingmay be applied to the electrocoated blank in as one coating composition,or, alternatively, the non-electrophoretic coating can be applied as amulti-layer composite coating. For example, a pigmented liquid firstfilm-forming coating composition as described in detail above can beapplied to at least one major surface of the electrocoated blank,followed by a subsequent application of a either a transparent ornon-pigmented (i.e., “clear”) liquid or powder second coatingcomposition. Likewise, a pigmented powder coating composition can beapplied to at least one surface of the electrocoated blank, withsubsequent application of a transparent liquid or powder coatingcomposition. In such cases, the coating station (4) can comprisemultiple coating application stations, for example a liquid spray boothin line with a powder spray booth, or vice versa. These coatingapplication stations can also include a drying station for drying (orcuring) the first non-electrophoretic coating prior to application ofthe second non-electrophoretic coating. Alternatively, the secondnon-electrophoretic coating can be applied directly to the firstnon-electrophoretic coating and the two coatings can be dried/curedsimultaneously.

The present invention is also directed to a process for forming amulti-composite coating on a pre-sheared, electroconductive, flat blankhaving two major surfaces and sheared edges. In this embodiment theblank is conveyed to a first electrodeposition bath (1) located on acoating line (A). Where a first aqueous electrodepositable coatingcomposition is applied to both major surfaces and the sheared edges ofthe blank as it passes through the first electrodeposition bath (1). Theblank serves as an electrode in an electrical circuit comprising theelectrode and a counter-electrode immersed in the aqueouselectrodepositable coating composition, the composition being depositedonto both major surfaces and the sheared edges of the blank as asubstantially continuous electroconductive coating as electric currentis passed between the electrodes. Optionally, the coated blank isconveyed from the first electrodeposition bath (1) to a first dryingstation (2) located on the coating line (A) where the electroconductivecoating is dried as it passes through the first drying station (2). Thecoated blank is then conveyed to a second electrodeposition bath (3)located on the coating line (A) where a second electrodepositablecoating composition is applied to the coated blank as it passes throughthe second electrodeposition bath (3). The blank serves as an electrodein an electrical circuit comprising the electrode and acounter-electrode immersed in the second aqueous electrodepositablecoating composition and the composition is deposited onto one of themajor surfaces of the coated blank as a substantially continuouselectrically insulating coating as electric current is passed betweenthe electrodes. The coated blank is then conveyed to a second dryingstation (5) located on the coating line (A); the electrically insulatingcoating is dried as the blank of step (6) passes through the seconddrying station (5).

It should be understood, that the first drying station (2) and thesecond drying station (5) can be the same or different drying systemslocated in the coating line (A). Likewise, if the first drying station(2) and the second drying station (5) are the same drying system, theshear (7A) and the shear (7B) can represent the same shear apparatus.

In the method described immediately above, electrodeposition bath (1)comprises an electrodepositable coating composition which forms anelectroconductive coating on both major surfaces and the sheared edgesof the blank. This electrodepositable coating composition can be ananionic composition or, as is preferred, a cationic composition. Theelectrodepositable coating composition from which the electroconductivecoating is electrodeposited onto both surfaces of the blank can be asubstantially unpigmented coating composition (i.e., a clearcoatcomposition) or a pigmented coating composition.

In one embodiment, the electrodepositable coating composition from whichthe electroconductive coating is deposited onto both surfaces of theblank comprises (a) an electrodepositable ionic resin, and (b) one ormore electrically conductive pigments. Non-limiting examples ofelectrodepositable ionic resins suitable for use in theelectrodepositable coating composition include the anionic and cationicfilm-forming polymers described in detail above, as well as thecorresponding curing agents for such ionic polymers.

The electrodepositable compositions can further comprise one or moreelectroconductive pigments to render the resultant coatingelectroconductive. Suitable electroconductive pigments includeelectrically conductive carbon black pigments. Generally the carbonblacks can be any one or a blend of carbon blacks ranging from thosethat are known as higher conductive carbon blacks, i.e. those with a BETsurface area greater than 500 m²/gram and DBP adsorption number(determined in accordance with ASTM D2414-93) of 200 to 600 ml/100 g. tothose with lower DBP numbers on the order of 30 to 120 ml/100 gram suchas those with DBP numbers of 40 to 80 ml/100 grams.

Examples of commercially available electroconductive carbon blacksinclude Cabot Monarch™ 1300, Cabot XC-72R, Black Pearls 2000 and VulcanXC 72 sold by Cabot Corporation; Acheson Electrodag™ 230 sold by AchesonColloids Co.; Columbian Raven™ 3500 sold by Columbian Carbon Co.; andPrintex™ XE 2, Printex 200, Printex L and Printex L6 sold by DeGussaCorporation, Pigments Group. Suitable carbon blacks are also describedin U.S. Pat. No. 5,733,962.

Also, electrically conductive silica pigments may be used. Examplesinclude AEROSIL 200 sold by Japan Aerosil Co., Ltd., and SYLOID® 161,SYLOID® 244, SYLOID® 308, SYLOID® 404 and SYLOID® 978 all available fromFuji Davison Co., Ltd.

Other electrically conductive pigments can be used, for example, metalpowders such as aluminum, copper or special steel, molybdenumdisulphide, iron oxide, e.g., black iron oxide, antimony-doped titaniumdioxide and nickel doped titanium dioxide.

Also useful are particles coated with metals such as cobalt, copper,nickel, iron, tin, zinc, and combinations of thereof. Suitable particleswhich can be coated with the aforementioned metals include alumina,aluminum, aromatic polyester, boron nitride, chromium, graphite, iron,molybdenum, neodymium/iron/boron, samarium cobalt, silicon carbide,stainless steel, titanium diboride, tungsten, tungsten carbide, andzirconia particles. Such metal-coated particles are commerciallyavailable from Advanced Ceramics Corp.

Other metal-coated particles which may be used advantageously in theelectrodepositable coating composition from which the conductive coatingis deposited include ceramic microballoons, chopped glass fibers,graphite powder and flake, boron nitride, mica flake, copper powder andflake, nickel powder and flake, aluminum coated with metals such ascarbon, copper, nickel, palladium, silicon, silver and titaniumcoatings. These particles are typically metal-coated using fluidized bedchemical vacuum deposition techniques. Such metal-coated particles arecommercially available from Powdermet, Inc.

Mixtures of different electroconductive pigments can be used.

The conductive pigment is present in the electrodepositable coatingcomposition in an amount sufficient to provide a conductive coatinghaving a sufficiently low specific resistance such that a secondelectrodepositable coating may be formed over the conductive coating.The amount of electroconductive pigment in the electrodepositablecomposition can vary depending on the particular type of pigment that isused, but the level needs to be effective to provide an electrodepositedcoating with a conductivity of greater than or equal to 10⁻¹²ohms/centimeter, more typically greater than or equal to 10⁻¹⁰ohms/centimeter, and usually greater than or equal to 10⁻⁶ohms/centimeter.

In other words, the conductive pigment typically is present in the firstelectrodepositable coating composition in an amount sufficient toprovide an at least partially dried (or cured) coating having a specificresistance of less than 10¹⁰, typically ranging from 10² to 10¹⁰ Ohmscentimeter, often from 10³ to 10⁸ Ohms centimeter, usually from 10⁴ to10⁶ Ohms centimeter.

As discussed above, the electrodepositable coating composition typicallyalso contains other pigments to provide corrosion resistance, hiding, oras fillers and additives such surfactants, flow additives and cratercontrol agents.

In the method of the present invention, once the conductive firstcoating has been applied to the blank, the electrocoated blankoptionally is conveyed from the first electrodeposition bath (2) to afirst drying station (2) located on the coating line (A) for drying theelectroconductive coating as it passes through the first drying station(2). Typically, the electroconductive coating is dried (i.e., cured) ata temperature ranging from 82° C. to 426° C., often from 150° C. to 275°C. for a period of time ranging from 60 to 1200 seconds.

The first electrodepositable coating composition is applied underconditions such that a substantially continuous conductive coatinghaving a dried film-thickness typically ranging from 0.1 to 0.4 mils(2.54 to 10.16 micrometers), often from 0.15 to 0.25 mils (3.81 to 6.35micrometers) is formed over both major surfaces of the blank.

In an alternative embodiment, the conductive coating is not dried orcured and the second electrodepositable coating composition is applieddirectly to undried coating on one major surface of the blank. This isgenerally referred to as a wet-on-wet (“WOW”) application. A wet-on-wetapplication is typically used where the first electrodepositable coatingis a transparent or clear coating which is substantially free ofpigment.

The coated blank is conveyed to a second electrodeposition bath (3) forapplication of second electrodepositable coating composition to form asubstantially continuous electrically insulating coating over one of themajor surfaces of the coated blank. The electrodepositable coatingcompositions discussed in detail above can be used.

As mentioned above, the blank having an electroconductive coatingapplied to both major surfaces is immersed in the secondelectrodepositable coating compositions and serves as an electrode,preferable a cathode, in an electrical circuit. The counter-electrode isplaced in very close proximity (that is, an interelectrode distanceranging from 2.5 to 25 centimeters) to the major surface to be coatedwith the second electrodepositable coating composition. When current isimpressed between the two electrodes, a substantially continuousinsulating coating is deposited on the major surface in close proximityto the counter-electrode.

Generally, application of the second electrodepositable coatingcomposition to only one major surface of the coated metal blank iscontrolled by limiting the “throwpower” of the second electrodepositablecomposition. By the term “throwpower” is meant the ability of anelectrodepositable coating to apply to or “wrap around” to recessed andshielded areas of a part or sheet of metal.

With reference to the above-described process, it should be understoodthat the second electrodepositable coating composition can “wrap around”the blank, depositing upon the edges and a portion of the major surfacewhich is not in close proximity to the counter-electrode (i.e., “theopposite major surface”). However, a substantially continuous insulatingcoating is not formed upon the opposite major surface.

The coated blank is then conveyed to a second drying station (5) locatedon the coating line (A) where the electrically insulating coating isdried as the coated blank passes through the second drying station (5).Drying or curing conditions are as described above.

In an alternative embodiment of the present invention, the pre-sheared,electroconductive flat blank having two major surfaces and sheared edgesis conveyed directly to the second electrodeposition bath (3) where anaqueous electrodepositable coating composition is applied to only onemajor surface and the sheared edges of the blank as the blank passesthrough the electrodeposition bath (3). It should be understood that theblank can be formed from a coiled metal substrate that is first suppliedto a shear located prior to the entrance of electrodeposition bath (3).The blank formed from the coiled metal substrate then can be conveyeddirectly to the electrodeposition bath (3) for application of theelectrodepositable coating composition onto one major surface of theblank. Coating conditions are as described above. The electrocoatedblank is then conveyed to the second drying station (5) where theelectrodeposited coating is dried as the coated blank passes through thesecond drying station (5). Drying or curing conditions are as describedabove for the electrically insulating electrodepositable coatingcomposition.

The present invention also is directed to various methods of formingcoated blanks from a continuous metal strip. The blanks can be formedfrom the metal strip initially, and the blanks then can be coated usingthe various coating methods as discussed above. Alternatively, thecontinuous metal strip first can be coated using the variouselectrocoating steps described above with regard to the pre-shearedblanks, and thereafter the blanks are formed from the coated metalstrip.

In one embodiment of the present invention, a continuous metal striphaving two major surfaces is supplied to the entrance of anelectrodeposition bath (1) located on a coating line (A). An aqueouselectrodepositable coating composition, such as those described indetail above, is applied to both major surfaces of the metal strip as itpasses through the electrodeposition bath (1), the metal strip servingas an electrode in an electrical circuit comprising the electrode and acounter-electrode immersed in the aqueous electrodepositable coatingcomposition. The electrodepositable coating composition is depositedonto both major surfaces of the metal strip as a substantiallycontinuous coating as electric current is passed between the electrodes.

With reference to FIG. 2, a suitable electrocoating apparatus 10includes an electrocoat tank 12 with a conveyor 14 extending at leastpartly into the interior of the tank 12. The electrocoat tank 12 may beof any conventional type and size to accommodate the substrates beingcoated for example, those described in U.S. Pat. Nos. 4,333,807 and4,259,163. The tank 12 is configured to contain an electrodepositablecoating composition such as the compositions described in detail above.

The interior of the tank 12 can be in flow communication with aconventional recycling system, to prevent solids in the coatingcomposition from settling to the bottom of the tank 12; a conventionalheat exchanger, such as an electric heater, in any conventional manner,to control the temperature of the coating composition in the tank 12;and/or a conventional ultrafiltration system to remove solubleimpurities from the coating composition and to recycle the filteredmaterial back into the electrodeposition tank 12.

As shown on the left side of FIG. 2, a load area 16 is defined adjacentone end of the conveyor 14. The load area has sufficient free space topermit unhindered loading of substrates to be coated, whether in blankor coil form, onto the conveyor 14 as described in more detail below.

The conveyor 14 has an inlet end 18 and an outlet end 20. The conveyor14 may be of any convenient type, such as, but not limited to, a beltconveyor, a chain conveyor, a platform conveyor, and the like. However,the conveyor 14 is typically composed primarily of non-conductivematerial so as not to attract electrodepositable coating material duringthe coating process. As will be appreciated by one of ordinary skill inthe art, the exemplary endless conveyor 14 shown in FIG. 2 provides anupper portion or leg to transport substrates during the coating processand a lower or return portion. As shown in FIGS. 2 and 3, the conveyor14 may be formed by a plurality, e.g., 5, of spaced, non-conductivechains 22 each movably mounted on rotatable wheels or sprockets 24 andsupported on guide rails to define a conveyor path P into and out of theelectrocoat tank 12. To help maintain a substrate on the conveyor 14during the coating process, a plurality of holding devices, for example,magnets, can be carried on the conveyor 14.

In order to electrocoat a substrate, the substrate should be under theinfluence of an applied electric potential. Therefore, a connectingsystem 26 is provided to connect the substrate to be coated to anelectrical source (not shown) during the coating process. In theexemplary embodiment shown in FIGS. 2-4, the connecting system 26includes a plurality of spaced, electrically conductive supports 28(FIG. 4) carried on the chains 22 and extending above the top or outersurface of the conveyor 14 to support and contact a metal substrateduring the coating process as described below.

A timing shaft (not shown) can be attached to the sprockets 24 so thatthe chains 22 move at substantially the same speed to maintain thesupports 28 in rows. Examples of suitable supports 28 for the practiceof the invention include K-1 electrical connectors commerciallyavailable from 3I Engineering of Evansville, Ind. Alternatively, thesupports 28 on adjacent chains 22 can be offset from one another, ifdesired.

In order to provide the electric potential, the supports 28 areconnected to one or more electrically conductive connectors. Forexample, the connectors can be solid, metal, electrically conductivegrounding bars 30 (FIGS. 3 and 4), each connected to one or more of thesupports 28. The grounding bars 30 can be carried on the chains 22 tomove when the chains 22 move. For example, one grounding bar 30 can beconnected to each of the adjacent supports 28 of a row as describedabove. Each grounding bar 30 may have an outer end 32, e.g., extendingabove the outer surface of the conveyor 14. So as not to clutter thefigures, only a portion of the total number of grounding bars 30 areshown in FIG. 2. The outer ends 32 of the grounding bars 30 define apath 34 shown in dashed lines in FIG. 3 as the conveyor 14 moves. Asdescribed below, the grounding bars 30 act to place one or more selectedsupports 28 in electrical contact with the electrical power to apply anelectric potential to a substrate carried on the selected supports 28when the selected supports 28 supporting the substrate are adjacent toor in the tank 12, particularly in a coating region of the tank 12, asdescribed in more detail below.

The grounding bars 30, e.g., the outer ends 32 of the grounding bars 30,are configured to contact an electrical bus bar 36 mounted adjacent,e.g., above, the electrocoat tank 12. As shown in FIG. 2, the bus bar 36is shaped, such that, as described in more detail below, the outer end32 of a grounding bar 30 contacts the bus bar 36 when the supports 28 towhich the grounding bar 30 is connected are positioned in or adjacentthe electrocoating composition in the tank 12 but loses contact with thebus bar 30 when the supports 28 connected to the grounding bar 30 passout of the electrocoating composition or out of the coating region ofthe tank 12.

As will be appreciated by one of ordinary skill in the art, theinvention is not limited to connecting systems having the grounding barand bus bar structure described above. For example, the connectingsystem 26 could be formed by a plurality of electrically conductivedriven contact wheels forming part of the conveyor or by opposed contactclamps configured to engage the substrate when located in the tank 12.Examples of suitable alternative connecting systems are disclosed inU.S. Pat. Nos. 4,385,967 and 4,755,271, herein incorporated byreference.

At least one and typically a plurality of first electrodes 40 arelocated in the electrocoat tank 12 on one side of the conveyor path,e.g., above the conveyor path as shown in FIG. 2. The first electrodes40 can be located less than 10″ (25 cm) from the top of the conveyor 14,i.e., the side of the upper leg of the conveyor 14 closest the firstelectrodes 40, are often less than 5″ (12.5 cm) from the top of theconveyor 14, and usually are less than 1″ to 2″ (2.5 cm to 5 cm) fromthe top of the conveyor 14. The first electrodes 40 can be attached toor carried on a vertically movable support (not shown) such that thedistance between one or more of the first electrodes 40 and the top ofthe conveyor 14 can be adjusted. The first electrodes 40 are disposed inthe tank 12 transverse to the conveyor path. The electrodes 40 areconnected to a power source (not shown) in any suitable manner, such asby cables. The electrodes 40 are made of electrically conductivematerial, such as copper, and may be configured as copper bars extendingacross the width of the conveyor 14 in the tank 12.

As described more fully below, one or more optional second electrodes 42can be located in the electrocoat tank 12 below the upper leg of theconveyor path P, e.g., opposite the first electrodes 40. If present, thesecond electrodes 42 are typically located 1″ to 10″ (2.5 cm to 25 cm)from the bottom of the upper leg of the conveyor 14. The secondelectrodes 42 also can be attached to or carried on one or more movablesupports such that the distance between one or more of the secondelectrodes 42 and the bottom of the upper conveyor 14 portion can beadjusted.

An exit rinse station 44 can be located at or near a discharge end ofthe tank 12. The rinse station 44 can comprise one or more sprayapplicators 45 in flow communication with a source of rinsing fluid,e.g., one applicator located above the conveyor path P of the upperportion of the conveyor 14 and one applicator 45 below the upper portionof the conveyor 14. For example, the spray applicators 45 can be in flowcommunication with the ultrafiltration system to provide permeate to therinse applicators 45. Excess rinse fluid can be directed into the tank12, e.g., by a sloped shelf located under the rinse applicators 45 andsloping toward the tank 12.

A first rinse station 46 is located downstream of the electrocoat tank12, e.g., downstream of the exit rinse station 44. The first rinsestation 46 can comprise any conventional rinse applicators but, in theexemplary embodiment under discussion, includes one or more sprayapplicators 48 located above and in flow communication with a firstrinse tank 50, e.g., by a pump and conduits to supply rinse fluid fromthe first rinse tank 50 to the spray applicators 48. The first rinsetank 50 may also be in flow communication with a conventionalrecirculation system having a recirculation pump (not shown). As shownin FIG. 2, one or more of the applicators 48 can be located above theupper portion of the conveyor 14 (and directed toward the outer surfaceof the conveyor 14) and one or more other of the applicators 48 can belocated below the upper portion of the conveyor 14 (and directed towardthe inner surface of the conveyor 14).

A first drain station 52 is located downstream of the first rinsestation 46 to remove at least some of the excess rinse composition fromthe surfaces of the substrate being coated. The first drain station 52can include one or more fluid removal devices, such as an air knife orsqueegee rolls. In the exemplary embodiment shown in FIG. 2, the firstdrain station 52 includes two air knives 54, with one air knife 54located above the conveyor path and another air knife 54 located belowthe conveyor path. The air knives 54 are configured to direct or blow atleast some of the excess rinse composition back into the first rinsetank 46.

A second rinse station 58 typically is located downstream of the firstrinse station 46. The second rinse station 58 can comprise anyconventional rinsing applicators but, in the exemplary embodiment underdiscussion, includes one or more spray applicators 60 located above andin flow communication with a second rinse tank 64, e.g., by a pump andconduits to supply rinse fluid from the second rinse tank 64 to thespray applicators 60 in similar manner as in the first rinse station 46.The second rinse tank 64 may be in flow communication with aconventional recirculation system having a recirculation pump (notshown).

A second drain station 68 is located downstream of the second rinsestation 58 to remove at least some of the excess rinse composition fromthe substrate. The second drain station 68 includes at least one fluidremoval device, such as one air knife 70 located above the conveyor pathand another air knife 70 located below the conveyor path. The air knives70 are configured to direct at least some of the excess rinsecomposition back into the second rinse tank 64.

A drying station 74 having a dryer 76 is located downstream of thesecond rinse tank 64 to dry and/or cure the applied coating. As usedherein, the term “dry” means the almost complete absence of water fromthe coating and the term “cure” means that the majority, preferably all,of any crosslinkable components of the applied coating material arecrosslinked. The dryer 76 can include any conventional drying oven ordrying apparatus, such as an infra-red radiation oven, an electric oven,a gas oven, a hot air convection oven, and the like. In one exemplaryembodiment, the dryer 76 is a high velocity gas oven commerciallyavailable from Gruenwald Corp.

The coated metal strip is then conveyed to a drying station (2) locatedon the coating line (A) where the electrodeposited coating is dried asthe coated metal strip passes through the drying station (2).Optionally, the coated metal strip is then conveyed to a recoilingstation located off the coating line and recoiled to await furtherprocessing. The coated metal strip is then conveyed (either from thedrying station (2) or from the off-line recoiling station) to theentrance of a metal shear (7A) located at an exit end of the dryingstation (2) and the coated strip is sheared to form coated blanks as thecoated metal strip passes through the shear (7A).

It should be understood that the blanks formed by the method describedimmediately above typically can have sheared edges devoid of anyprotective coating. Hence, the method optionally can comprise theadditional steps of applying corrosion inhibitive chemicals to thesheared edges. Examples of suitable corrosion inhibitors can include,for example, yttrium acetate.

In another embodiment of the present invention, a continuous metal striphaving two major surfaces is supplied to the entrance of anelectrodeposition bath (1) located on a coating line (A). A firstelectrodepositable coating composition, such as any of theelectrodepositable coating compositions which provide anelectroconductive coating described in detail above, is applied to bothmajor surfaces of the metal strip as it passes through theelectrodeposition bath (1). The metal strip serves as an electrode in anelectrical circuit comprising the electrode and an counter-electrodeimmersed in the first aqueous electrodepositable coating composition,the composition being deposited onto both major surfaces of the metalstrip as a substantially continuous electrically conductive coating aselectric current is passed between the electrodes. Optionally, thecoated metal strip is conveyed to a first drying station (2) located inthe coating line (A) and the electrically conductive coating is dried onthe metal strip as it passes through the first drying station (2).Optionally, the metal strip coated with the electrically conductivecoating can be transferred to a recoiling station located off-line toawait further processing.

The metal strip coated with the electrically conductive coating isconveyed (either from the first drying station (2) or from the off-linerecoiling station) to an entrance of a shear (7A) located adjacent anexit end of the drying station (2). The coated metal strip is thensheared to form a coated blank as it passes through the shear (7A).

The coated blank is then conveyed to a second electrodeposition bath (3)for application of a second aqueous electrodepositable coatingcomposition, such as any of the electrodepositable coating compositionsdescribed above, to one of the major surfaces of the coated blank as itpasses through the second electrodeposition bath (3). The blank servesas an electrode in an electrical circuit comprising the electrode and acounter-electrode immersed in the second aqueous electrodepositablecoating composition. The composition is deposited onto one major surfaceof the coated blank as a substantially continuous electricallyinsulating coating as electric current is passed between the electrodes.

The electrically insulating coating is electrodeposited onto one majorsurface of the blank as described above by positioning thecounter-electrodes in close proximity to the major surface to be coated.Likewise, it should be understood that the electrically insulatingcoating typically “wraps around” the blank, coating the edges and aportion of the opposite major surface as described above.

The coated blank is then conveyed to a second drying station (5) locatedon the coating line (A), and the electrically insulating coating isdried as the blank passes through the drying station (5).

In another embodiment, the continuous metal strip is supplied to anentrance of an electrodeposition bath (1) located on the coating line(A) and a first electrodepositable coating composition is applied asdescribed above to both major surfaces of the metal strip as it passesthrough the bath to form a continuous electrically conductive coating onboth major surfaces of the metal strip. Optionally, the coated metalstrip is conveyed to a first drying station (2) and the electricallyconductive coating is dried as the metal strip passes through the dryingstation (2). Upon exiting the drying station (2), the coated metal stripcan be transferred to a recoiling station located off-line to awaitfurther processing. Alternatively, the coated metal strip is conveyed(either directly from the electrodeposition bath (1) for a WOWapplication, from the drying station (2), or from the off-line recoilingstation) to a second electrodeposition bath (3) located on the coatingline (A). A second electrodepositable coating composition is applied asdescribed above to one of the major surfaces of the coated metal stripas it passes through the second electrodeposition bath (3) to form asubstantially continuous electrically insulating coating on one majorsurface of the coated metal strip.

The coated metal strip is then conveyed to a second drying station (5)located in the coating line (A) and the coated metal strip is dried asit passes through the second drying station (5). Optionally, the coatedmetal strip is then transferred to a recoiling station located off lineto await further processing. Alternatively, the coated metal strip isconveyed (either from the second drying station (5) or from the off-linerecoiling station) to an entrance of a shear (7A) or (7B) located at anexit end of the drying station (2) or (5). The coated metal strip issheared to form coated blanks as the metal strip passes through theshear (7A) or (7B).

In an alternative embodiment of the present invention, the coiled metalstrip is conveyed directly to the second electrodeposition bath (3) forapplication of an electrodeposition coating composition to only onemajor surface of the metal strip as the metal strip passes through theelectrodeposition bath (3). The metal strip is immersed in the secondelectrodepositable coating composition and serves as an electrode,preferable a cathode, in an electrical circuit. The counter-electrode isplaced in very close proximity (that is, an interelectrode distanceranging from 2.5 to 25 centimeters) to the major surface to be coatedwith the second electrodepositable coating composition. When current isimpressed between the two electrodes, a substantially continuousinsulating coating is deposited on the major surface in close proximityto the counter-electrode. Application of the second electrodepositablecoating composition to only one major surface of the metal strip iscontrolled by limiting the “throwpower” of the second electrodepositablecomposition. Also, it should be understood that the secondelectrodepositable coating composition can wrap around to the majorsurface of the metal strip which is not to be coated, provided that asubstantially continuous coating is not formed thereon.

The coated metal strip is then conveyed to the second drying station (5)where the coating on one major surface is dried as the metal strip passthrough the second drying station (5). Optionally, the coated metalstrip can be conveyed to a recoiling station located off the coatingline (A) and recoiled to await further processing. 120. The coated metalstrip can be conveyed directly from the second drying station (5) or,optionally, from the recoiling station, to an entrance of a shearlocated at an exit end of the drying station, for shearing the coatedmetal strip to form a flat coated blank as the strip passes through theshear (7B).

As aforementioned, metal blanks coated by the methods of the presentinvention can be “post-formed” into parts to be assembled into variousend-products, for example, front, side and back panels for appliancessuch as washers, dryers and refrigerators. The post-forming processes(e.g., punching and bending) require that the coatings (including themulti-layer composite coatings) which are applied to the blanks beparticularly adherent and flexible.

In one embodiment of the present invention, the electrodepositablecoating is a post-formable coating capable of providing a T-bendflexibility rating of less than 6T, typically ranging from 0T to 6T, andoften ranging from 2T to 4T as determined in accordance with ASTM-D4145.In another embodiment of the present invention, the electrodepositablecoating is a post-formable multi-layer composite coating capable ofproviding a T-bend flexibility rating of less than 6T, typically rangingfrom 0T to 6 T, and often from 2T to 4T as determined in accordance withASTM-D4145.

Illustrating the invention are the following examples which are not tobe considered as limiting the invention to their details. Unlessotherwise indicated, all parts and percentages in the followingexamples, as well as throughout the specification, are by weight.

EXAMPLES

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but itis intended to cover modifications which are within the spirit and scopeof the invention, as defined by the appended claims.

Examples A Through B

The following Examples A and B describe the preparation of cationicelectrodepositable conductive primer compositions useful in theprocesses of the present invention. Example A describes the preparationof pigmented electrodepositable conductive primer coating compositionand Example B describes the preparation of an unpigmentedelectrodepositable conductive primer coating composition. Eachconductive primer composition is in the form of an electrodepositionbath. Each of the electrodeposition bath compositions was prepared byblending under mild agitation the following ingredients:

Example A Example B Ingredients (parts by weight) (parts by weight)CR661¹ 1326.33 1500.00 CP639² 445.82 — Deionized 2027.85 2100.00 Water¹Electrocoating resin component available from PPG Industries, Inc.²Electrocoating pigment paste component available from PPG Industries,Inc.

The electrodeposition bath composition of Example A had apigment-to-binder ratio (“p/b”) of 0.15 and a total solids content of17.0 percent based on total weight of the respective electrodepositionbath compositions. The electrodeposition bath composition of Example Bhad a total solids content of 15.0 percent based on total weight of theelectrodeposition bath.

Example 1

This example describes the preparation of an electrodepositable topcoating composition for application over conductive electrodepositableprimer compositions in the processes of the present invention. Theelectrodepositable top coating composition is in the form of anelectrodeposition bath composition. The electrodeposition bathcomposition was prepared by blending under mild agitation the followingingredients:

PARTS BY WEIGHT INGREDIENTS (grams) CR940B¹ 1352.07 CP436² 375.88Deionized water 2072.05 ¹Electrocoating resin component available fromPPG Industries, Inc. ²Electrocoating pigment paste component availablefrom PPG Industries, Inc.The resulting electrodepositable top coating bath composition had atotal solids content of 15.0 percent based on total bath weight and ap/b of 0.53.

Example 2

This example describes the powder top coating composition forapplication over conductive electrodepositable primer compositions inthe processes of the present invention. The powder top coatingcomposition is a dry powder coating composition, PCT80139W, commerciallyavailable from PPG Industries, Inc. of Pittsburgh, Pa.

Comparative Example 3

This comparative example describes application of a conventional liquidcoating system. The liquid coating system was comprised of a liquidurethane primer coating, APPPY 3020, with subsequent application of aconventional liquid polyester topcoat, APTW 3952. Both the APPPY 3020and the APTW 3952 are commercially available from PPG Industries, Inc.of Pittsburgh, Pa. The conventional liquid coating compositions wereused as the control series to be evaluated versus the electrodepositablecoating compositions applied by the methods of the present invention.

Test Panel Preparation:

Each of the above-described electrodepositable conductive primer bathcompositions (Examples 1 and 2) was applied to cold rolled steel (“CRS”)test panels, which had been pretreated with CF710 CS20®, a zincphosphate pretreatment composition commercially available from PPGIndustries, Inc. The pigmented primer coating of Example A waselectrodeposited at 15 seconds/1.75 Amps/175 volts onto the zincphosphated CRS, the non-pigmented coating Example B was electrodepositedat 60 seconds/1.0 Amps/100 Volts. Each primer coating composition waselectrodeposited at film builds ranging from 0.15 mils to 0.35 mils(3.75 to 8.75 micrometers) dry film thickness.

The electrocoated test panels for Example A were baked at a temperatureof 400° F. (204° C.) for 20 minutes to cure the conductive primerthereon. The electrocoated test panels for Example B were then “flashed”for 5 minutes at room temperature to allow dehydration to occur.

The electrodepositable top coating composition of Example 1 was thenapplied to the primed test panels prepared as described immediatelyabove. For Example A, (cured conductive primer), and Example B,(air-dried conductive clear coat), the electrodepositable top coatingcomposition of Example 1 was electrodeposited at 90 seconds/1.2 Amps/125Volts. The top coated panels thus prepared were then baked at atemperature of 350° F. (177° C.) for 20 minutes to cure theelectrodepositable top coating composition. The cured top coatingcompositions had a dry film thickness ranging from 1.20 to 1.4 mils (30to 35 micrometers).

The powder top coating composition of Example 2 was then applied to theprimed test panels. For Example A (cured conductive primer), and ExampleB (air-dried conductive clear coat), the powder topcoat composition ofExample 2 was applied by electrostatic spray. The top coated panels thusprepared were then baked at a temperature of 400° F. (204° C.) for 10minutes to cure the powder topcoat. The cured powder topcoat compositionhad a dry film thickness ranging from 1.20 to 2.20 mils (30 to 55micrometers).

With respect to the conventional liquid coating system of Example 3, theprimer APPY 3020 was roll applied to zinc phosphate treated galvanizedsteel substrate, then cured at a temperature of 400° F. (204° C.) for 10minutes. A dry film thickness of 0.2 mils (5 micrometers) was achieved.The liquid topcoat was then spray applied to the primed substrate andcured at a temperature of 400° F. (204° C.) for 10 minutes to form atopcoat having a dry film thickness of 0.8 mils (20.3 micrometers).

The test panels thus prepared were evaluated for corrosion resistance bysalt spray testing in accordance with ASTM B17; detergent resistance inaccordance with ASTM D2248; and flexibility by T Bend testing inaccordance with ASTM D4145 (where 0T=best; np represents no pick off;and nc represents no cracking.)

Test results are reported below in the following TABLE 1.

TABLE 1 Salt Spray Conductive Flexible Top Corrosion Detergent PrimerCoat Resistance Resistance Flexibility Example A Example 1 1.5 mm totalNo blisters 2T np 3T scribe creepage nc Example B Example 1 3.0 mm totalFew #8 blisters 3T np/nc scribe creepage Example A Example 2 0.5 mmtotal No blisters 3T np/nc scribe creepage Example B Example 2 0.5 mmtotal Medium #8 2T np/nc scribe creepage blisters Not Example 3 2 mmtotal <few #8 4T np/nc applicable (compara- scribe creepage blisterstive)

The data presented in Table 1 illustrate that the two coat process ofthe present invention provides flexibility properties, 2T np and 1T ncbetter than the comparative prepaint control system applied byconventional processes. The two coat systems of the present inventionusing Example A as the primer and Examples 1 and 2 as the flexibletopcoats provides better detergent and salt spray performance thanExample 3, the comparative prepaint system applied by conventionalprocesses.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but itis intended to cover modifications which are within the spirit and scopeof the invention, as defined by the appended claims.

1. A method for coating a continuous metal strip and thereafter forminga coated blank therefrom comprising the following steps: (1) supplying acontinuous metal strip having two major surfaces to the entrance of anelectrodeposition bath located on a coating line; (2) applying anelectrodepositable coating composition to both major surfaces of themetal strip as it passes through the electrodeposition bath, thecontinuous metal strip serving as an electrode in an electrical circuitcomprising the electrode and a counter-electrode immersed in theelectrodepositable coating composition, the composition being depositedonto both major surfaces of the continuous metal strip as asubstantially continuous electrodeposited coating as electric current ispassed between the electrodes; (3) conveying the continuous metal stripfrom step (2) to a drying station located on the coating line; (4)drying the substantially continuous electrodeposited coating as thecontinuous metal strip passes through the drying station to form acoated metal strip; (5) optionally, conveying the coated metal stripfrom step (4) to a recoiling station and recoiling the coated metalstrip to form a recoiled coated metal strip; (6) conveying the coatedmetal strip from step (4) or, optionally, the recoiled coated metalstrip of step (5) to an entrance of a shear located at an exit end ofthe drying station; (7) shearing the coated metal strip from step (6)or, optionally, the recoiled coated metal strip of step (6) to form aflat coated blank as the coated metal strip or, optionally, the recoiledcoated metal strip passes through the shear; and (8) forming the coatedblank from the flat coated blank of step (7).
 2. The method of claim 1,wherein the continuous metal strip is contacted with a pretreatmentcomposition prior to step (1).
 3. The method of claim 2, wherein thepretreatment composition comprises a zinc phosphate composition.
 4. Themethod of claim 1, wherein the electrodepositable coating compositioncomprises: (a) an active hydrogen group-containing electrodepositableionic resin, and (b) a curing agent have functional groups reactive withthe active hydrogen groups of the ionic resin (a).
 5. The method ofclaim 4, wherein the active hydrogen group-containing electrodepositableionic resin is electrodepositable on a cathode.
 6. The method of claim5, wherein the active hydrogen group-containing electrodepositable ionicresin comprises cationic onium salt groups.
 7. The method of claim 5,wherein the active hydrogen group-containing electrodepositable ionicresin comprises cationic amine salt groups.
 8. The method of claim 4,wherein the active hydrogen group-containing electrodepositable ionicresin is electrodepositable on an anode.
 9. The method of claim 8,wherein the active hydrogen group-containing electrodepositable ionicresin comprises anionic acid salt groups.
 10. The method of claim 1,wherein the substantially continuous electrodeposited coating comprisesa post-formable coating capable of providing a T-bend rating of lessthan 6T.
 11. A method for forming a coating on a continuous metal stripand thereafter forming a multi-layer composite coating on a blank formedtherefrom, the method comprising the following steps: (1) supplying acontinuous metal strip having two major surfaces to an entrance of anelectrodeposition bath located on a coating line; (2) applying a firstelectrodepositable coating composition to both major surfaces of thecontinuous metal strip as it passes through the electrodeposition bath,the continuous metal strip serving as an electrode in an electricalcircuit comprising the electrode and a counter-electrode immersed in thefirst electrodepositable coating composition, the firstelectrodepositable composition being deposited onto both major surfacesof the continuous metal strip as a substantially continuous electricallyconductive coating as electric current is passed between the electrodes;(3) optionally, conveying the continuous metal strip from step (2) to afirst drying station located on the coating line, and drying thesubstantially continuous electrically conductive coating as thecontinuous metal strip passes through the first drying station to form acoated metal strip; (4) optionally, conveying the coated metal strip ofstep (3) to a recoiling station located off the coating line, andrecoiling the coated metal strip; (5) transferring the coated metalstrip from step (2), or, optionally, step (3) or step (4) to an entranceof a shear located at an exit end of the drying station; (6) shearingthe coated metal strip to form a flat coated blank as the continuousmetal strip passes through the shear; (7) conveying the flat coatedblank from step (6) to a second electrodeposition bath located in thecoating line; (8) applying a second electrodepositable coatingcomposition to one of the major surfaces of the flat coated blank as itpasses through the second electrodeposition bath, the flat coated blankserving as an electrode in an electrical circuit comprising theelectrode and a counter-electrode immersed in the secondelectrodepositable coating composition, the second electrodepositablecomposition being deposited onto one major surface of the flat coatedblank as a substantially continuous electrically insulating coating aselectric current is passed between the electrodes; (9) conveying theflat coated blank of step (8) to a drying station located on the coatingline; (10) drying the substantially continuous electrically insulatingcoating as the flat coated blank of step (9) passes through the dryingstation; and (11) forming a coated blank from the flat coated blank ofstep (10).
 12. The method of claim 11, wherein the continuous metalstrip is contacted with a pretreatment composition prior to step (1).13. The method of claim 12, wherein the pretreatment compositioncomprises a zinc phosphate composition.
 14. The method of claim 11,wherein the first electrodepositable coating composition comprises: (a)an electrodepositable ionic resin, and (b) one or more electricallyconductive pigments.
 15. The method of claim 14, wherein theelectrodepositable ionic resin is electrodepositable on a cathode. 16.The method of claim 15, wherein the ionic resin comprises cationic oniumsalt groups.
 17. The method of claim 15, wherein the ionic resincomprises cationic amine salt groups.
 18. The method of claim 14,wherein the electrodepositable ionic resin is electrodepositable on ananode.
 19. The method of claim 18, wherein the electrodepositable ionicresin comprises anionic acid salt groups.
 20. The method of claim 14,wherein the one or more electrically conductive pigments comprises oneor more particulate materials selected from the group consisting ofblack iron oxide, graphite, conductive carbon black, molybdenumdisulphide, polyaniline, conductive silica, antimony-doped titaniumdioxide, nickel-doped titanium dioxide and mixtures thereof.
 21. Themethod of claim 20, wherein the one or more electrically conductivepigments comprises conductive carbon black.
 22. The method of claim 14,wherein the one or more electrically conductive pigments is present inthe first electrodepositable coating composition in an amount sufficientto provide an electrically conductive coating having a specificresistance of less than or equal to 10¹⁰ Ohms centimeter.
 23. The methodof claim 11, wherein the specific resistance of the electricallyconductive coating ranges from 10³ to 10⁸ Ohms centimeter.
 24. Themethod of claim 11, wherein the second electrodepositable coatingcomposition comprises: (a) an active hydrogen group-containing ionicresin, and (b) a curing agent having functional groups reactive with theactive hydrogen groups of the active hydrogen group-containing ionicresin.
 25. The method of claim 24, wherein the active hydrogengroup-containing ionic resin comprises cationic onium salt groups. 26.The method of claim 24, wherein the active hydrogen group-containingionic resin comprises cationic amine salt groups.
 27. The method ofclaim 24, wherein the active hydrogen group-containing ionic resincomprises an acrylic polymer having cationic onium salt groups.
 28. Themethod of claim 11, wherein the multi-layer composite coating comprisesa post-formable multi-layer composite coating capable of providing aT-bend rating of less than 6T.
 29. A method for coating a continuousmetal strip comprising the following steps: (1) supplying a continuousmetal strip having two major surfaces to the entrance of anelectrodeposition bath located on a coating line; (2) applying anelectrodepositable coating composition to one major surface of thecontinuous metal strip as it passes through the electrodeposition bath,the continuous metal strip serving as an electrode in an electricalcircuit comprising the electrode and a counter-electrode immersed in theelectrodepositable coating composition, the electrodepositable coatingcomposition being deposited onto one major surface of the continuousmetal strip as a substantially continuous coating as electric current ispassed between the electrodes; (3) conveying the continuous metal stripfrom step (2) to a drying station located on the coating line; (4)drying the substantially continuous coating as the continuous metalstrip passes through the drying station to form a coated metal strip;(5) optionally, conveying the coated metal strip from step (4) to arecoiling station and recoiling the coated metal strip; and (6) forminga coated blank from the coated metal strip of step (4) or from thecoated metal strip of step (5).
 30. The method of claim 29, furthercomprising the steps of conveying the coated metal strip from step (4)or, optionally, the coated metal strip of step (5), to an entrance of ashear located at an exit end of the drying station, and shearing thecoated metal strip to form a flat coated blank as the strip passesthrough the shear.